As been said before:

[1] Ergo vs. STI - Rider preference

[2] Campy drivetrain vs. Shimano drivetrain - Campy doesn't seem to shift quite as smooth as Shimano but smooth enough (for most people). Shimano doesn't seem to last quite as long as Campy but long enough (for most people). It's a wash here in terms of performance. Campy does look prettier though (at least to me) but I then again don't (or shouldn't) stare at my derailleurs when I'm riding the bike.

[3] Campy crank vs. Shimano crank vs. other manufacturer's cranks - I think performancewise, at the very top-end, it's also wash. I'm sure my FSA cranks perform on par with Campy Record-C and Shimano Dura-Ace. After that it's all aesthetics... and price. The Campy cranks cost twice as much and the Shimanos cost about the same. The issue here is that if you went with OctaLink, you'll most likely be forced into buying Shimano's BB and D-A BB's have been criticised for their durability problems. I know many of the touring guys go with Ultegra BBs instead of D-A even if the rest of the bike is D-A. Ugliness aside (and I do think the 2004 D-A cranks are ugly), the new D-A cranks even further solidifies the need to run only one combination of crank and BB. Maybe this will change over time and I hope it does but unfortunately it looks like this is a solution in search of a problem. The MTB crowd never fully bought into the Bullseye crank concept and they're tough on their components. Those who'll want to mix and match will most likely stick with ISIS for a long time... until another open standard comes along.