We're building an application for OS X, and we can't rely on our users all having upgraded to Snow Leopard, or whatever the latest version is. We want to make sure that as many people as possible can use our app, but we also don't want to throw away some improvements that were made in OS X version if only 1% of users are stuck using earlier versions.

Is there anywhere I can find information on the proportions of people that are using each version of the OS? Or is there some "common wisdom" on the issue that real mac developers know?

We don't need any superfancy graphics or 3d animation stuff, just plain old windowing APIs - but we've already run into one problem where "NSStreamDelegate" isn't supported prior to snow leopard.

Thanks!