Hmm, you mean it might be hard to get a good sound if you're not using it solely as a pre-amp for a power amp? I guess I should've mentioned what gear I have now, come to think of it: I've an ENGL Fireball (a kind of budget version of the Powerball) with an ENGL cab, and a (heavily tweaked) Lexicon which I use as pre-amp, effects device and just about everything else (it's a guitar processor, pretty much all-in-one).
Personally, I think I've tweaked that Lexicon just about as far as it can go. As a tone freak who's in love with the guitar sound of people like Petrucci, or the kinds of sounds you hear on most prog productions, I just feel I need a lot more clarity, crunch, thickness, etc. The higher strings sound too thin, rhythm is too muddy, and I still have a bit of background hiss I can't get rid of. Basically what I'm hoping for is that the POD can give me that rectified sound without actually having to go for a Mesa amp. Also, the prospect of having access to a whole range of great guitar sounds is very inviting. What I'd like to do is use that POD the way I've been using the Lexicon - plug it into the Fireball (clean channel), since it's a tube amp anyway. Without that Fireball, that Lexicon gain would've sounded like crap, I think.