Well Dean,
That's an excellent question and I can say they are great for rentention are a great add on to sites. All the major paysites have them and for a good reason.
Your best best is ask for a free month of gamming content from
www.xamo.com and let them track the game plays for you.
It's important that you make a bad ass games room and make it very aware to your members. ThAT GAMES ARE HERE!! dont hide them. GET screen shoots of each game and link to them that way.
Talk to Ron at
www.xamo.com for futher information,
from cost, bandwidth, niche of game, and prizes offered to members.
I hope you get games for surfers love playing them. They are always an overlooked piece of content.