The PODxt seems to constantly get updates. It has the GuitarPort functionality, USB connectivity, and loadsa tones from customtone.com. You can buy the model packs for it to get even more amp and effects for it, and everything is easy to upgrade using the Line6Monkey.
That said, POD 2.0 is easy to use, has great sounds and bags loadsa tones on custometone.com too. Okay, it isn't the latest product, doesn't have the USB connection, and doesn't offer the GuitarPort functionality, but you have to ask yourself whether you are going to use them or not.
I find the PODxt easy to use, keep up to date and obtain patches for. I still haven't got round to reading the manual, but have tweaked several settings through just figuring things out through simple use.
I like the fact that you can do everything through the software without actually having to touch the dials on the actual PODxt.
So, to summarise, both units will offer great tones and patches can be obtained from custometone.com. PODxt just has more features available (with the addition of the model packs), and has the USB functionality and GuitarPort functionality built in.
If you're gonna make use of all these extra features, then go for it. However, I would advise you play around with one first, or get both a PODxt and a POD 2.0 if you can, in case you don't like it...
I know there are many users on this site that are morwe than happy with their POD s.0's, and get great results from them too !!!
Good luck !