They're fun - provided you have the right kit, i.e. reasonably fast glass or if the lighting's appalling (as it often is in pubs), an external flash with a portable soft box attached, and dial the flash right down to keep it natural instead of super bright.
A few from the last gig:
I've been after Jim's hair toss - third time lucky
The drummer asked me to get him twirling his stick... half way to success:
Drummer in motion: