I wouldn't worry about this at all. I have had literally hundreds of card accounts (thanks for the tips, FTers!) and have never had any real problems with getting more cards and bonuses and getting a mortgage when needed.

By the way, there is no need to pay off your card accounts in full each month to keep your credit in good shape. Making the minimum pay on time will suffice--but, of course, will run up high interest charges which is a big no-no.