While I think credit cards have great benefits (see stevenwei for an excellent summary), getting the card does have a consequence in my experience: every card I've ever had has an annual maintenance fee (perhaps not the case in the USA?).
While this sucks for the system as a whole, on an individual level it does mean that those of us who have a reliable income (or FU money) can use credit cards very differently. They provide convenience, consumer protection, usually some kind of 'reward' (travel points or such), and yes, a 30 day grace period in which you can do something else with your money though I usually don't think of it that way. In fact, from an individual standpoint the only reason I can think of to use a debit card rather than credit here is a complete lack of financial responsibility/will power.