I strongly suspect that we're looking at a late-August, early September release. Not for technical reasons, but because Apple will want to avoid colliding with the iPhone 3G release on July 11th - both because of publicity, and because of crowds in the stores.
I don't get the iPhone fascination (both because of lousy AT&T and the device itself), but enough do that Apple will probably milk the free advertising for at least a month, then release a speed-bump with the new CPU's, new GPU's, and maybe (if we're very lucky) new screens.
Given that we haven't seen any new MBP identifiers in 10.5.3 or in 10.5.4 yet (although I presume folks aren't done searching), we may also have to wait for 10.5.5, or it won't include a new GPU (which would suck), and just be a CPU change.
There's a VERY slim chance may release on July 8th or 15th to cross-sell macs to iPhone buyers (and vice-versa), but I highly doubt it.