It is an excellent all-rounder.
Pretty good camera, bluetooth, infra-red, polyphonics and java games. Call quality is excellent and so is the screen... which leads onto its bad points. The screen in direct sunlight is very hard to see (as you'd expect, but it is worse than most phones), java performance is pretty bad but capable and the menus can be a bit slow. I have also noticed that some text messages cause it to lag too. I do however, have the very first edition of this phone and much of those fault have been rectified in firmware updates. You'll get recent firmware if you buy it new, or it can be updated at service centers.
There are also some great sites for T610 games, themes, ringtones and wallpapers (myt610.net, being one) and esato.com has a huge sonyericsson forum full of helpful people =)