Just got back from a trip to Cancun for the weekend, and I've learned a few things:

No matter how technologically advanced we get as a civilization, you still need to carry a pen.
Laws should be written with some semblance of intelligence assumed in the people. Things move a lot quicker.
I appreciate the ability of US Airports to publish their gate number assignments more than 50 minutes before flight time.
I can appreciate why people get buzzed socially. Still don't know if I enjoy it that much, though.
It's quite possible to walk around for 10 minutes and find 8 different USD-MXN exchange rates. It is also mathematically impossible to make any money playing the exchanging game between those vendors.
The US Dollar is starting to suck.
When relying on SPF50 suntan lotion, be sure you get every square inch of your body. I have an interesting sin(x)/4x shaped line down my back (with the 0 near my right shoulder)
If you're going to visit a foreign country, at least attempt to learn some aspect of the language before you visit. Baño, bien, y tu, para ti, and gato only take you so far.
Bodyboarding is still freakin awesome.
As is snorkeling. We saw 3 dolphins in 30m deep ocean!
Take more shirts then you think you'll need.
The intracity buses in Cancun are 6.50 MXN, roughly 60 cents US. Freakin nuts!!

There's probably a few more, but those are the ones I remembered to write down on my phone between planes.