It's been about a week since Valve opened Steam for Mac to the public and the company has followed up with some usage statistics. The developer reports that around two thirds of all Steam Mac users are running on a laptop, which isn't a shock considering the popularity of Apple's MacBook line. Portal supposedly crashes one fifth as often on Macs as on PCs, and that isn't terribly surprising either since there are fewer hardware configurations.
There is one detail that we wouldn't have guessed, however: in only 7 days, more than 11% of all Steam purchases are for the Mac. We're not sure if this suggests that Mac-compatible titles (which are also for PC) account for 11% of purchases, or if that figure actually represents Mac players. Shacknews expects the company to release more stats in the future, so hopefully that will be made clearer.