I got to the Vegas strip about 20 hours ago but I haven't done any of the quests there yet.  Am I near the end of the main story or is there still a ways to go?  I ask because I don't really want to play the game once I've hit the level cap, so I initially avoided anything having to do with the strip.  Now I'm at level 24 and I'm thinking it's probably about time to start wrapping things up.

There are several places where you will have to start making decisions and choices.
The main storyline is not very long at all, and requires you to do some secondary quests so how far away from end are you will depend on some of the stuff you might have already done.
I would personally consider endgame to begin when you walk into the casino to confront Benny, as that is when your choices really start to matter in regards to the main storyline, but even after that point there is still plenty to do and choices to make. It's not quite straight forward. The actual point of no return (when you get cut off from the game world) is at the very very end after you already burned bridges.