Sometime in the future I may just be insane enough to go with DA-7900 DT shifters, 10 Speed cassette and chain. For about $170 that will upgrade me from 8 - 10 speed. I'm figuring a few years riding with the 8 speed DT system and then I'll decide if brifters are worth it. I'd probably only settle for the Ultegra-6700 group if I go that way and then you have do it en-masse since there are numerous compatibility issues with brakes, chain sizes etc.

PS. From the research I've done incl. Sheldon Brown's site, a nine speed chain should work great with my setup (8 speed cassette, Ultegra SL derailleurs, vintage 53/44 crankset). I'll be trying it sometime this week or the weekend at the latest - HG-93 and PT Master Chain puller are poised and ready to go.