Of course the preset guys don't know what's going to be played through it, but having played the preset patches through my BKP'd guitar, a high-end strat and a high-end Les Paul, I can safely say that it didn't really make much of a difference. Of course they all sounded different in themselves, but as for the sound quality of the presets, no matter what I plugged into it, they sounded poop.
However, once you have a good tweak for an hour or so, you can come up with several patches that really own. It's always well worth taking your own guitar to the shop, testing the POD out, and fiddling with a user patch to create your own sound. That way you get a much better understanding of the unit's potential. I have the XT Live, and the next step for me is either the Axe FX or the new Pod HD (depending on how much I can save, heh.)