What d'you plan on spending your money on? You're staying at an all inclusive and that seems like a fair whack of cash for spending money (or perhaps I'm just tight and should rephrase that to say it seems like a lot of money to *me*!).

If you're planning on lots of excursions, most of them take credit cards which is definitely the most convenient route but bear in mind that most cc co's have a charge for foreign transactions (although they're usually sneaky about it and bury in the rate, so it's not easy to see). You'll want to check what yours charges and make sure you OK with that.

Another option is to leave your cash at home and use ATMs to withdraw pesos as and when you need them. Of course, this is only viable if your bank doesn't have high charges for foreign withdrawals (I know some UK banks are really bad in that regard).

If you do bring cash, most resorts offer a money exchange service but their rates vary - some are great, some not so much. You can also exchange your money at a bank or cambio where you'll usually get the best rates (but if you have to take a taxi to get there, you have to factor that into the cost).

As for tipping in dollars, your prerogative of course but I don't bother with US money at all. I just use pesos for everything - much easier than juggling three currencies. With respect to spending cash, I get enough pesos before I leave home to last me a couple of days and then just withdraw more from ATMs as required. Easy peasy and I don't have to carry wads of cash around with me (or stash them in the room safe).