BUY ALREADY!
Software companies, unlike many people here, realize that the majority of Mac users are not MacRumors addicts who check message boards 3 times a day watching for updates!

Example: the two graphic designers I work with didn't even know about Tiger until I told them Monday! The software companies of the world realize how many users are "in the dark" with regards to updates, and I don't think they will be so foolish as to stop selling software to these people within the next 3-4 years.
As for me, a portion of the $4,000 I was prepared to spend on a PowerMac/ACD setup was instead used to buy a PowerBook. It will easily get me through to the time when the Rev. B Intel PowerMacs are released. And at the point when I buy one of the new desktops, the PB's portability will be a nice compliment for the new system. Even then, with the 2-3 years of age, it will still be perfect for travel - as email, web surfing, watching DVD's on planes, and light design work are not really intensive activites.
For those wanting to buy now, I suggest not going with a pricey high-end machine/display setup unless you need it. Go with a cheaper Mac Mini or portable, as either would be a nice supplement to a new desktop down the road - the Mini as a media center, or a portable for...well...portability! And their lower prices will ease the sting a bit on the day the Intel Macs are rolled out!
I am currently looking forward to using a Mac for the first time in over a year (since I left my company-owned PB behind at my last job!) and actually owning my very first! And even more pumped that, as of Monday when my new beauty arrives, this 6 year old clunker Dell is heading for the closet!