I'm using MIUI on the Nexus One, and its really slick.
Basically what MIUI does is that it makes it look as close to the iOS as possible. The menu structure, the settings, the overall UI is made and changed completely to resemble the iOS. Even the menus are changed to white and the on/off toggles of the iOS are used.
The main reason why I use it though is that it also changes the stock apps. Again, making them resemble the iOS. But some of them is really good, for example, the dialer looks exactly like the one in iOS and includes smart dial and the likes. As well as the SMS app.
Some things are modded to give it a unique feel too. Like for example the stock music app is changed to MIUI's own one. It automatically searches for lyrics, has folder play, and even has a visual EQ. That EQ even displays on the lockscreen in real time, and is smooth, not laggy.
Of course, it might not be everyone's taste, since it basically resembles the iOS so much.

Added on January 28, 2011, 10:07 amQUOTE(Savor_Savvy @ Jan 28 2011, 09:31 AM)
looking for good quality screen protector and casing...any recommendation?
btw, for ap set, can we register ourselves at the htc e-club? although my set is ap, but my imei is the same with the imei on the box. i thought ap set, the imei won't be the same?
Then you're lucky. They used the box that came with your phone. The reason why most ap sets' is different is because they usually take a random box with a random phone. Like sometimes you bought a white phone but the box they gave you states its black.
Casings? Otterbox is always my answer
This post has been edited by Calex: Jan 28 2011, 10:07 AM