Buy one now if you want it. Seriously. Barring armageddon, there will always be something better to wait for, and these machines were just updated last week. They were nice. The are nicer. If you want a Mac, you'll be very happy with your purchase.
In my own opinion, Apple will slowly phase out the standard resolution displays in their next refresh; they might do this mid-cycle depending on their plans. I recall they did starting to phase out the 1680x1050 display in their 17" 2 years ago when they started offering a 1920x1200 display. Of course the former was CCFL backlit and the latter LED backlit, but I see Apple moving in that direction.
Apple will not want to upset customers, so they'll probably not update in 2 months time. 😉