If you have a lot of old media (old VHS or even the few and far between DVD with only pro-logic or DD 2.0) you might appreciate it. Pro logic 2 does seem to provide a fuller environment than the original pro logic.
My own personal preference is to use prologic 2 for old 2 channel movies. I use it for cable TV too, but I wouldn't be heartbroken without it.
For music, I still prefer stereo to any of the other 2 channel processings for most of my discs, but for the few and far between that I do like surround processing, I prefer DTS:Neo Music to Pro logic 2 music settings.
So I guess in short, it's not a bad thing to have, but if I were without it completely, I wouldn't be rushing out to upgrade. If you're interested in a receiver that doesn't have it, I would get the receiver regaurdless. It's not worth sacrificing a sound that you've fallen in love with just to gain processing that really only enhances old material.