I have used MM a bit. Some nice models and it appears to very well organised but as with any of these web based models sites, you will get your fair share of flakers and no shows.
Some of the photo retouchers are excellent.
MY Profile
Just been approved by Model Mayhem in 48 hours but Pure storm can't be bothered after a week.
http://www.modelmayhem.com/1636086
I tend to find purestorm better for finding models tbh, and I like how you can rate them (esp the non-shows) on there.
http://www.purestorm.com/profile.aspx?id=_belial
Am on MM as well, and have managed to arrange a few shoots through it, just wish they'd make it a bit more feature rich :0
http://www.modelmayhem.com/739248
I'm on there too, but have not used it much.. I am going to make a more concerted effort to get some shoots organised in the coming months though..
PS added you all as friends..
I've just registered on both MM and purestorm
Meeeeeee http://www.modelmayhem.com/698530
I was on purestorm but I closed my account as the forums were overly bitchy and the quality of work on there wasn't as inspiring as over on MM. Plus I kept getting messages from girls with mobile phone/myspace style images and shoot requests from known flakers.
Lots of girls wanting to get their their bbies out over on purestorm though, if you're into shooting that sort of thing.