Hooking up randomly is very different with hooking up with people that you see on a semi-regular basis (no matter how little or many there are). I don't count kissing or making out as hooking up either. There's kissing (single), feeling up (double), hooking up (triple), and then well, you know. (and he hit the home run!)
Feeling up -- clothes stay on (hence the second base part).
Hooking up -- clothes come off (hence the third base part).
Those are my definitions.
Kissing, feeling up, or hooking up randomly does not necessarily make for a slut either. Sometimes a hook-up is just a hook-up. It's when either the guy or the girl has a lot of sex with a lot of strangers that may be kind of slutty (so the amount of relationships one has had does not equal sluttiness).
Either way, when it comes to dating, I don't judge what others do, by the way. I just try not to go where every man's gone before.