I walked home from the colegio this morning and used the following greetings with various people as they passed by:
buenos dias (good morning)
buen dia (good morning)
buenas (variation on good morning)
que tal? (how's it going)
adios (mix between goodbye, farewell, literally -to God)
I'm perplexed as to how people decide to use, as everyone uses a different one with me. I heard all of these from them and merely replied in kind.
Everyone greets everyone here. If you come into a room of 30 people, you shake everyone's hand - and again when you leave. It is courtesy so common that if you don't do this people wonder why you jilted them.
It's good though, lots of smiles each day. Unless someone waves to you while you're ripping down a hill with huge potholes and speed bumps and chickens on your bike - then it could prove lethal.