The latest version of CSS is here. But should I change over? Can someone tell me why I should/shouldn't and what are the extra features available in CSS3?
No it's not. It's still mostly in development, with very little browser support, though some of its modules have been implemented in bits by various browsers—for the most part accessed by vendor-seific prefixes like -moz- and -webkit-.
There's not reason not to experiment with these, but because browsers don't support much of CSS3 yet, you either have to find workarounds for older borwsers or just accept that some users will get an ehanced experience.