So I'm heading to Cancun in a couple of weeks for a conference and I've never been down there at all. Who can give me a heads up as to what to expect, avoid etc. I've got no plans yet, just attending the talks and well, drinking a lot.

I'll be staying here.

go see the Mayan ruins in Tulum and Coba! Totally awesome.

Seconded. But you'll need to rent a car to get to either place. Tulum is an hour or so south of Cancun, and Coba is about 90 minutes inland from Tulum.

I stayed in Tulum in March of last year - very tranquil, beautiful place. I don't think you could stay there and not feel relaxed. The only noise at night is the sound of the surf. I'd go back. I avoided Cancun, b/c it seems like a really touristy, Spring-break Mecca.

Thirded. Did Chichen Itza instead of Tulum, but the ruins are amazing.

-expect to take a lot of watery shits
-pick up some over the counter valium...but hey, why stop there, get a small quantity of heroin since you're able to.
-make sure you bring cash to bribe crooked mexican cops whien you get caught fucking a donkey on the beach

Now this is sound advice. Ruins, shit, dope and bribes.