I had a Midiverb 4 that I used for recording and loved it Never really used it for guitar much though I thought the reverb in it was great and it was identical to the Quadraverb reverb at the time.
I see both used in Guitar racks quite often so some seem to like it.
I just picked one up on ebay, but only had it running through my Tremoverb for about a 1/2 hour. I think it worked ok. I got mine for about $80 - but this past wknd saw one at a local shop for $55 - DOH!!
If anyone else has experiences/tips I'm interested. Hopefully this wknd I'll get more time to tool around.
There's definitely better units out there now, but this is the old school Shoegazer staple, so I was pretty psyched to get one.