krizrox: Well, I've had a chance to use the PSY-Q on a couple of mixes. I have to tell ya, this is a nice tool to have. It came out just at the right time for me since I'm in the process of mixing and mastering a recording project for a local rock band.  This is a great tool if you have a rather dull sounding mix (would be great on some old analog cassette tape restoration I'll bet). I've been using it primarily on some vocal tracks and it's worked great! It really adds some nice - smooth sounding - sparkle. It can make a track sit in the mix a little better. I didn't notice much of a difference on the bass tracks. This thing is clearly happiest with a mid-range or full-range signal.  If your overall mix is already tight and bright sounding, you probably don't need this. But if the mix or track seems a little dull and lifeless, this will work wonders. Since I prefer to use things like this sparingly, I will probably pull it out only for individual tracks that seem to need a little spice. The vocalist I'm working with at the moment has kind of a lazy monotone-ish quality to his voice. It fits the music OK but sounded kind of dull. The PSY-Q changed that instantly.

dblbass: Decent explanation of the basics of 'Exciters' are given here and on how to use them here.

Janni:  I use PsyQ and bx_digital to fatten up the stereo image and avoid phase issues.  If you use other techniques you might have to check mono compatibility.