Numerous websites have been reporting that Snow Leopard will be demoed at MacWord '09 in January, along with some benchmark speed comparison data. But it will not be released to the general public until later.
However, they also have stated that Apple is planning to release it BEFORE WWDC '09.
That may be the plan now, but plans for OS releases almost always seem to change. So who knows if it actually will be out before WWDC or not.
Steve said on stage at WWDC '08 that Snow Leopard would be out in about a year, so that could be before or after WWDC '09. A vague wide window.
I would expect a similar comment during MacWorld '09's demos. He'll probably say something like, "it will be out this summer."
The bigger question is how much will people that buy new Macs right now have to pay to upgrade? And if programs also need to be updated to take advantage of the new efficiencies, how much will those upgrades cost?
People who are looking to buy a new Mac soon will want to know those things.
It looks to me just like with Tiger, they may announce sometime early next year, may be even MacWorld 09, and then set the release date for late April (I guess it was 29th April for Tiger). That would be about an year, that Jobs talked about. Just a guess.