I'm really struggling with this. I've brought myself the frame pictured at the bottom of the post - a Serotta CHT. Triple butted titanium and some of the nicest welds in the industry. It's also (yippee!) got a disc mount.
Now, I suppose I was originally thinking of building it up a bit retro style (it's probably important at this point that I note it'll be my only mountain bike). The trouble is, the price of retro parts has been creeping up steadily for a couple of years now. When you get them, they're secondhand and there's no guarantee something won't snap or otherwise fail.
Wiggle and Merlin are in the middle of a bit of a price war right now. For about Â£1000 I could get a full M960 XTR groupset, SID Teams, a DT 240 wheelset, Chris King headset and some reasonable finishing kit. Cracking value, and a great bike.
The trouble is the modern kit still leaves me cold - it's boring and functional. It's much more fun searching out retro parts. I suppose what I'm saying is I'm a retrobiker at heart, but I feel torn between the fun stuff and practicality!