actually the answers to your ques are on the first post of this thread
well, i can say the super amoled screen is nais 

loudspeaker on sgs is fine. loud enough.

sgs: IMO, most beautiful because of super amoled. you need to see the screen in person. the rest are normal lcd screen. rooting, custom roms are plain easy.
DHD: bigger screen with same resolution with sgs, thus will be a bit less dpi.
htc desire: i recommend this over sgs for my parents I would not let my parents tinker with root and custom roms, odin, and deal with RFS    A good all round phone. Have big support with the community. Got cyanogenmod too.
se x10: software will not be up to date (officially). better wait for newer SE smartphone. have beautiful customized interface but users will suffer with lack of update to froyo,

i guess it's on par.. compared with my sis's iphone and sounds almost the same :/

1. You could just totally not set any APN (or destroy any APN set for you). On Froyo, you can disable data connection. The apps and system will still attempt to connect to internet periodically but would fail. To obtain best experience with smartphones, a data plan is highly recommended. To me, the phone is boring (I don't play games), it's just the online contents and convenience that attracts me.

2. OS does not update over wifi for now. KIES would not wipe your personal data usually. The usual way of setting up an Android phone is to sync contacts and calender to Gmail account. Android phone also allows Microsoft Exchange server connection for corporate accounts. In any chance of contacts and calender being wiped, just setup those accounts and information will be fetched automatically, provided you have internet connection.

3. The difference between them aren't just the display. Both firmwares are not cross-flashable, hence I believe they are quite different hardware internally.

have u try read the 1st post? i believe there are many info that u can find at there..

i think what noobie1 said to look to 1st page of this thread not the 1st thread..   

ok if.. anything you don't understand...just pop-up here..there will be somebody to answers the questions

http://www.mobile88.com.my/cellphone/Samsu...4.0/preview.asp

nice back cover..but unfortunately doesn't fit in our sgs

---

Added on March 10, 2011, 10:48 am

1. yes..you can go to setting and set the apn to mms only..then your phone will not transmit data...and you can update any app or email using wifi only...

2. you got 2 options to upgrade to 2.3..one via samsung kies or via flash thru odin

3. if you download an apps from market...it will automatically install in you phone or it will prompt you to install automatically when download is finished

4. if you install other launcher ..the original touchwiz is still there and you can swap with other launcher..u can use apps called home home switcher for froyo..search in the market...

hope this will help you...cheersss..

go for xperia neo..