I need a Macbook by early June. I'm thinking about getting an MBP. Should I buy now, or wait to see if there's an update to come out within the next two months?
Buy now. You won't see a new case design for at least 3 years. The next update will likely be in October, prior to the holiday season. All you'll see there is possibly a speed bump/bigger hard drives? Possibly a different graphics card?
A year? Apple won't leave the specs alone for that long.
I expect them to bump the speed one more time before Intel launches the Arrandale processors. They'll probably go 2.8 GHz / 3.06 GHz on the MBP sometime this summer. Then there's the Snow Leopard launch in September -- nothing to do with hardware specs but you save a few bucks if you hold out for the next OS. In Q1 2010 they'll get the grand Arrandale treatment, and this may or may not include USB 3.0 ports which is probably the most significant paradigm shift in the pipeline as far as laptops go (it's not like you can update them by adding an USB 3.0 adapter).
Having said that, if you need it by June, you don't have time to wait for any of the upcoming updates I mentioned anyway, so get it now.