Here's my question though: why? Apple's sitting as pretty as you can sit in this economy, and Snow Leopard is already a huge hit even before it leaves the gate (it's coming before Windows 7, it's easier to figure out, and it's certainly a whole lot cheaper). So why would Apple do something so character-breaking as to start showing off by releasing software early? If there were bugs or problems with it, and they released it early, wouldn't that come back around to hurt them even worse?
If you ask me, Apple isn't going to push it -- they said September, their schedule probably allows for September, and they won't have any issues with waiting until September. They may release it early, but you'll have to color me surprised: we'll probably see it in September.