Currently I have several cards due to having a life that's very internationally split, between the US/France/UK mostly, with bank accounts in each, plus (in the

Currently I have several cards due to having a life that's very internationally split, between the US/France/UK mostly, with bank accounts in each, plus (in the US at least) separated accounts for business/personal. I have 3 US credit cards as well, one business and two personal -- the second is just a backup for if the first fails (and when I'm traveling, they fail frequently). It doesn't cost anything to have a new card (if you don't carry a balance), so it's useful to have a backup. 30 cards sounds like someone with a serious debt problem. Separate credit/debit cards are a really useful distinction -- in particular, I can maintain much higher security for my debit cards (and not use them online); a credit card purchase can be disputed without the money already being gone from your account. But they're certainly dangerous (given how people tend to rationalize spending money they don't have...), and carrying a balance on a credit card almost certainly means you're doing something wrong. They make it really easy to live beyond your means; I got burned by that a couple of years out of college, clawed my way back out of debt over a few years (fortunately with reliable income and low expenses!) and haven't made the same mistake again.