Hey, I wrote this on another post so please forgive the cut and paste. The Buyers guide is solely a function of avg days between upgrades. It does not in any way factor in speculation of rumors, external issues like the ending of relationships with Nvidea, or availability of Core 2 Duos, etc. That said an 8 month release for an Air has happened before, and June releases of laptops in time for back to school occur very often (as you'll see from the buyers guide). The buyers guide formula works well if Apple updates a product with regular frequency, but breaks if it is sporadic or if no historical data exists.
The most recent rumor i know of was the AppleInsider article from April 22nd. I think typically the closer you get to the rumored date, the more credible the rumors become. So far we haven't heard anything to the contrary. The rumors say they will start to be produced by the end of May. If true we can expect some more leaks and rumors in the next week or two.