I just bought the Pod HD400 to replace my trusty Vox Tonelab which I'd been using as my main recording setup for electric.
I'm still getting to know the HD400, and I've got to say that these amp models are very good. The technology is getting better and better all the time.
The real acid test for me was when I was able to get some very realistic Fender Twin and Deluxe models that sound & feel close to the real thing. Most of the amp modelers will do decent high gain sounds but the cleaner/semi-dirty sounds seem to be what separates the great modelers from the average ones. I was able to dial in some great sounds for surf and rockabilly with my HD400 and having fun with them. I'm also finding the looper feature to be a useful tool to use for writing, as a way to try a few parts against each other before I record them.
The Pod HD not the easiest interface to use, for a live setup, but it seems doable (haven't tried to us it that way yet). I think that the Vox modeler had a more straight-forward interface as a live setup, (easier to tweak on the fly), but the PoD sounds more realistic, now with these updated models. I'm really liking mine overall.
--Jim