ASC1951 said:
I don't understand why this question comes up every few months. Why would you want to mix them? Why not just decide which you prefer - Campag in my case - and stick to that?
For me, a few different reasons:
Cost - using a 105 cassette, hubs, and rear mech will save a lot of money in the long run, about £20 every time I change cassette and £30+ for rear mechs.
Longevity - I'm confident that shimano cassettes etc. will still be widely available for 10 speed in another 10 years. Try finding anything pre-9 speed for campag without paying through the nose.
Flexibility - My shimano hub will take a 10 speed road cassette or, if needs be, a 9 speed mtb cassette for lower gears (no worries with shifter compatibility as I have a shiftmate).
Noise - A Campag freehub would just vex the living hell out of me.