It's the same old argument with the PC components industry. If you wait, you'll get either better stuff for the same price, or the same stuff for a cheaper price... But when the new stuff actually arrives, then suddenly there's some <i>even better</i> stuff around the corner... and so on ad infinitum.
There's no easy solution to this really, you just have to pick a time, bite the bullet, and buy the stuff you think you need at the time.
My personal opinion would be either buy a 2.4C now and overclock it - making sure you get a good quality mobo which will hopefully support one of the first prescotts should you need it - or wait for the prescott chips to come out, and take advantage of suddenly cheaper high-end northwood chips (3.0C or 3.2C).
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$hit Happens. I just wish it would happen to someone else for a change.