on my 7D with only 30MB/s cards I can shoot 21 LJPG in a row on HSC, the canon official spec says only something like 15 shots.
wait until you get the 1d mk5 or alleged 1ds mk4 with 8fps 32mp, then you're going to need the fastest card you can get, i think SanDisk are doing well if they can get these on the shelves now so pros can buy them before (or with) their next bodies.