Old thread, but just to add a data point from 8/2010.
$50 Initiation fee (this seems to vary with current promotions- this was for August)
$145 monthly fee (use at one location); i believe it was $175 for all locations.
Plat got the following benefits on top of standard new members:
5 Additional Training Sessions (making 6 total, plus a fitness evaluation)
1 50-minute massage at their spa
Annual offer of 2 free sessions when you buy 6.