Ok, so I bump charge my battery and it's performing better now. 
After the bump charge, I did some extreme battery draining activities just to test it out:-
1) downloaded 157MB of data through Wi-Fi for the Let's Golf game (it's currently free from Gameloft, BTW)
2) Played a couple rounds of golf.
3) Updating facebook, crusing round the forums with Tapatalk.
4) Sent a couple of emails
5) Trying out the new ADW launcher themes.
6) Made and answered a couple of calls and SMS (normal day-to-day usage)

Around the 12th hour, I still had 63% left on my battery. A full 24-hours and it was at 42%. This is just amazing. When I first used FroYo, the phone would never lasted that long. I'd say without me 'going to town on WiFi and playing 3D games' the battery should last like 2days or more.

Anyways, here's how you bump charge your battery with battery calibration steps embedded. If you're not rooted and have no way of wiping the battery stats, I suppose you can just ignore the step. 

1.) Connect the phone to the charger with the phone powered on, and allow the phone to charge until the notification LED is green, indicating the device is fully charged (use OS Monitor to make sure its at 100%.)
2.) Disconnect the phone from the charger, and power it off.
3.) Reconnect the phone to the charger with the phone powered off, and allow the phone to charge until the notification LED is green.
4.) Disconnect the phone from the charger and power it on and wipe battery stats, then reboot.
5.) Once the phone is powered completely on, power it off again and reconnect it to the charger until the notification LED is green for a minimum of 30-60 minutes.
6.) Disconnect the phone, power it on, and use it.

Here are a couple of things to note on my phone setup. They may or may not affect my battery performance results:-
[*] I have Juicedefender running
[*] I run an undervolted kernel. A somewhat unstable one I might add. I grabbed a nightly build from intersectRaven's file dump before realizing that he hasnt officially released it yet. And I'm kinda lazy to re-flash a stable kernel. 

That depends on your setup like how many widgets are you using, do you have live wallpaper on etc. An indication that you may need to bump charge your battery is when all of a sudden you feel that the battery life gets shorter even though you're using your phone normally. Let's say that you normally get 1.5 day, out of the blue it dropped to 0.5 day. Your battery then either needs to be recalibrated or it is physically damaged. A total recalibration would be to discharge the battery totally, partial charge, wipe the battery stats and recharge it to full power. But that would need a root permission or some crazy looking adb commands (at least to those outside the Linux world), so HTC came up with this bump charging method that is more suitable for all users (with or without rooted device).

Anyways, EVO 4G is an awesome phone but with a terrible battery life (as reported by its users). Here's a post detailing how to fix it. There are probably some tips in there that may apply to other HTC sets:-
http://www.cloudave.com/link/fixing-the-ba...-evo-incredible

Another unproven myth is that task killers can improve battery life. This has been debated in countless occasions. Do task killers really help? Or is it just a placebo effect? Does it do more harm than good? Here are some good threads on the issue, read them if you have the time and you decide:-
http://androinica.com/2010/05/07/google-an...-are-pointless/
http://www.google.com/support/forum/p/andr...87bb09cba&hl=en
http://forum.xda-developers.com/showthread.php?t=683176
http://forum.legendroid.com/android-genera...-on-your-phone/

I used task killer on my 1.5 Hero. It did help in releasing memory and maybe prolonging the battery life a bit. But since going to 2.1, I didnt see any difference using a task killer in terms of battery life. In fact, on Eclair, I found that my phone was lagging whenever I have the task killer on. So, I abandoned it. On FroYo, task killer is made more redundant as FroYo's memory management is just fantastic. You'll get twice as much free memory than on Eclair.

If you charge it during off state and it straight away go green, it is at full capacity. Anyways, if you want a more detailed report on how your battery is faring, go to the Market and look for 'OS Monitor'. If you go to the 'Misc' tab you'll see some info about the battery. If you see 4000mV and you're around 90% capacity or more. Then the battery is fine, generally speaking.

Here's the good part though, something that can measure whether bump charging will have any effect on your batt. Go to the 'Message' tab and click the 'menu' button on your phone. Choose 'Option' from the pop-up menu and scroll down until you see the 'Message' section. In the 'View Log' option choose 'dmesg'. Tap 'Filter dmesg', check 'Enable Filtering', tap 'Tag Filter' and type 'batt' in the text box. Get out from the 'Options' (press 'back' a couple of times) to the 'Message' tab. You'll now see a more detailed stats of the battery condition, including the rate of it discharging. Apply some common sense here, a Desire/Nexus battery is 1400mA (it's actually more but HTC rounds the figure). So if your condition is at 100% and you see the reading is below 1400mAh (like 1300mAh or something worse), then you'll need to bump charge it and reset the battery stats as it is obviously giving the wrong reading. Some guys on XDA managed to get it up to 1480mAh through bump charging. That mAh is actually an indicator on how much juice your battery has. The more, the better.

Ah, the old 8 hour-charge myth. That only applies to dinosaur age Ni Cad batteries not the current Li Po batteries. Years and years of misinformation by those vendors and nothing has changed  What I do is charge (untill it fully charges or 2.5hrs-max is fine) and discharge the battery fully for the first 4-5 usage cycles to condition the battery so that the phone can read the battery level accurately. After that you can bump it or just charge your battery as often as you can which will improve the battery life (tip for X10 from Sony Ericsson). I have my usb charger at work and a cigarette charger in the car which I plug in all the time so I never have to worry about battery life

well, iPhones Battery Drains very fast, i use an iphone, but when u upgrade the latest firmware the battery life increases and becomes a longer lasting 1 , so if ur buying an iphone, upgrade it to iOS4.0.1

It works on Eclair too as it is more to hardware than software. Just that the dmesg batt output on Eclair is raw and a hassle to read, unlike Froyo where it is formatted to display in units (mAh and mV). I guess I'll snoop around my old Hero and see if I can come up with a way to translate those weird numbers to comprehensible figure.
And we can swap batteries too. 
While iPhones can only rely on software updates to improve its battery life, Androids have wider options for the task. We can do it through software (e.g undervolting the kernel) or hardware (e.g buying extra battery). 

I've done active surfing for that past hour and my X10 battery is still 100%. WTF?