Lots of people like them but I hate them, sold by XT and some other stuff and bought a Rocktron Prophesy II (the best pieve of gear I have ever owned - no need to upgrade ever again) - it is so insanely far ahead in terms of what it can do and the sounds it can make IMO. However, its all in the ear of the beholder. Try the POD out in a music shop using headphones (not through a massive rig with a tube poweramp) - that's what it will sound like at home.
I would recommend the Boss GT8 and GT-Pro, the Vox Tonelab and the Digitech GNX4 as being ahead of the PODxt for realism. The one thng the POD xt wins hands down in the customer supprot and downloadable features and upgrades - very impressive but not enough to swing my overall vote.