if you're looking at carbon Zipp 404's then a word of warning. on our recent bike trip to Colombia, one of the guys had a set on his Pinarello - the front wheel lasted 3 days before it fell apart. the roads in Colombia were not a lot worse than many of the UK's finest with potholes galore, although at times the road surface would disappear altogether!!
in summary, they may not last the course if you use them for training - fine for racing on smooth roads, but not for everyday use imho.
as an aside to that - his Pinarello frame also eventually failed - it was a top end carbon one and the chainstay broke. shall we say, he had an expensive trip......
so - carbon is fine but make sure it can stand the rigours of everyday riding on crappy road surfaces
also on the trip we had one bike with Di2 shifters (on a Cervelo P2) - that lasted the trip fine and I don't think the rider had any problems. BUT if something had gone wrong she would have been stuffed trying to get it fixed in Colombia as dealers and mechanics for it are as rare as rocking horse crap. so again - if you go electronic, look at where you ride it and what backup is available if something goes wrong.
and as a further aside - both the Pinarello rider and the Di2 rider were medics. more money than sense maybe???
Edited: 09/01/2012 at 10:23