In reply to Martin1978: I'm going to say, more than doubles in the U.K is bit over the top. But then again when you climb that splitter crack in america you will be borrowing everyone's cam of that size. If one of your tripples is a bit old and past it then you probably could ditch that if you wanted a bit of spare cash.
I'd work out what cams I liked best and then treat the others as doubles, i.e Dmm's as your mainstay then heliums when you need a bit more of that size or visa versa.
At the moment I have dmm dragons, 00-6. Then doubles of 2 and 3, the two being a cragswag camalot. This works well, I may eventually double up on other sizes with camalots when necessary. btw the dragon 6 is rarely used, rarely taken up, to save weight. Don't bother with a cam of this size until you want to do a route where you need it.