I'm going to the one in St Petersburg this June.
The line-up is OK. Not too exciting... going for the experience, really. Some friends said they had a good time last year. Flights were dirt cheap and I'm only going up there for the day so it's practically just another night out.
St. Pete lineup:
FEEL (RU)
TOCADISCO (GER)
FEDDE LE GRAND ( NL)
MEGAMIX
DEADMAU5 (CAN)
SANDER VAN DOORN (NL)