Zero commercial MMOs. Zero non-commercial MMOs. Several MMP attempts. Mine is the only one AFAIK that comes even close.

I've been working for years on this questions and my latest prototype has been tested up to 50 people with a theoretical capacity (based on computer resource load) of hundreds more. However our system is not stable and it has some bugs that prevent us from publishing.

Advice: with the slew of new MMO solutions out there (Multiverse, Second Life, Realm Crafter among others), it is not worth your time attempting this on GS at this time; there are much better MMP solutions on the market today as opposed to 5 years ago when I started down this path.