My SMIL got one for my little two girls last year (3&4). It's a neat idea, but my girls would much rather ride their REAL bikes and they aren't into video games at all so it was a bust. I sold it on Craigslist with the Dora and Barbie game for less than half the retail.
Pros - neat concept, keeps kids active during winter in colder climates (we have a milder climate, snow isn't unheard of but it isn't the norm and doesn't stick around when it does happen), improves gross motor skills, eye/hand coordination, spatial relations, physicality. Easy for the kids to figure out on their own
Cons - graphics are awful given the available technology, soundtrack loop is parentally annoying, the cord that connects to the bike is in two parts, one connects to the tv/stereo system, then connects to the other cord which is permanently attached to the bike. It would be very nice if this part disconnected completely from the bike for storage. Limited ammount of games. Games have a hole in the cartridge to connect the cartridge to the 'key ring', but the 'key ring' will only hold 3, maybe 4 games - an onboard storage somewhere (maybe the back?) would be nice.
If you're not concerned with second hand and want a good deal on the bike - try Craigslist. In my area there are several for sale between $40 -$70.