IMO it is probably worth waiting. Even if you don't immediately take advantage of DDR400 or 8x AGP, you'll be much happier later when you do decide to upgrade and you don't have to replace your MB again.
I'm still waiting for Serial-ATA and benchmarks for AMD's Hammer processors.
personally, i think its best to buy at "the tail end of a technology" as you put it, b/c all the bugs have been worked out and its less expensive. you have to ask yourself if what you are doing is really going to warrant DDR400 vs 333? concidering you can run games just fine with a p3 700 and a nice graphics card, id go with the less headaches and take the money you save and go buy some beers.
....the birds seemed to be calling him, thought caw....