I don't know what the heck I was smoking before when I tried this and failed, but I take back everything I said before about not being able to get a good bass tone on the POD HD.

I spent a little time with my P-Bass and HD400 and dialed in a tone for my bass that's rich, lively, and sounds great.  Like many of you, bass is not my primary instrument, but I do need the ability to lay down a groove with at least one good bass tone.  This is worth at least $100 to me in some other gear I can now get rid of, since I can count on my POD HD for a good bass tone!

Of course this is using the Bassman amp and cab model.  I think my problem before was the mic selection.  I don't remember if I just didn't change it from the default or what, but the only mics that didn't sound overly guitarish to my ears were the condensers, the 87 model being my choice.

Here's a link to the HD400 patch at customtone:

http://line6.com/customtone/tone/208049/