The story posted a couple months ago about Apple ordering both 15.4'' LED and 13.3'' LED backlit screens said that the 13.3'' were ordered for 3Q 2007 and the 15.4'' were for Q2 2007. The 15.4'' was right and the MBPs got the LED screens in June.
If this report is correct for the 13.3'' also, then we'll be targeting October - November for the next Macbook revision with the Santa Rosa platform and LED screens. It won't be before October because of the back-to-school promotion, and Apple won't change the main product during the promo.
So I'm guessing Macbooks get the next revision in October or November and possibly the Macbook Pro getting a slight speed bump to 2.4/2.6. Then the Macbook Pros will get Penryn in March or so.
The Macbooks are definitely getting LED displays in the next update though. 13.3'' is a common size and they are already readily available for a cheap price. (17-30'' for iMacs, MBPs, and ACDs are harder to come by and also much more expensive right now.)