WARNING! Obnoxious and adult language, but still worth watching...
http://www.youtube.com/watch?v=0p4fkH9qC4MI keep hearing the question about diamonds on mcoms, and while it's a valid question I thought this video might point out other things you won't pick up on if you've never played non-HC or at least not at length.
For instance, Q (by default) is used to spot enemies, assign squad goals (attack/defend mcom, etc.) and also to ask a buddy for some ammo/medic/repair.... In HC, spotting is a joke (can't wait for medium-core), but all these other things are useful and help in communicating with people that aren't on TS.