Tribute bands.

What's everyones thoughts on Tribute Bands?
There are a number of good tribute bands out gigging. a few that spring to mind are:

Regenesis - Heard them recently play the whole of the Lamb album complete with original slide show and lights. Really good gig. I took my wife along and she thought it was like a HUGE musical therapy session with all these 40something guys singing along to EVERY track........I WAS Rael for a couple of hours so maybe she was right.

Fragile - Very good Yes covers band. Their album is worth a listen as they add their own arrangements to the songs without drifting too far from the originals.

The Muffin Men - Great Zappa type band.

Anyone know of any others worth checking out?