One more thing: if you carry a dozen of them, yes, I can see how you may have a problem keeping track of everything. But if you focus on just one or two cards with very high limits, then it’s easy. I only have two, and I don’t actually use them (just got the cash, set up automatic minimum payments, and tossed them in a drawer, activation stickers still on them). Also, I don’t know about “rolling over”, as I haven’t been doing this long enough. But, if these offers will still be around a year from now, I might think about that. If not, I’ll just pay the balances back and close the accounts.
Finally, it goes without saying that balance transfer fees are a no-no (why pay a 3% fee now to get a measly 5% in a year?). But most cards don’t charge that for their “special offers”.