i stopped waiting on the date of the macbook event. I was disappointed on their MB/MBP update so I decided to get an iMac instead since I would've used the MBP as a desktop replacement anyway. 24" LED lcd would be nice but there really is nothing wrong with the current display, and I doubt there will be dramatic cosmetic change, if any, anyway. The new iMac will probably use the Nvidia chipset and run a slightly faster CPU along with DDR3 ram. Specs-wise the new iMac will be faster than the current gen (duh!) but it all depends on what you gonna do with it. If you're not using it for intensive graphical work then I'd say difference in performance is not really noticeable.
ohh and since nobody has said it in this thread, allow me to do so: if you need it now then buy. If you don't, wait. 😀