My favorite quote from the comments on this discussion about what is the optimal time to arrive at a party:
This only works if all guests judge by the same criteria. They do not. In many circles, late arrivers are seen as lazy, irreponsible, disorganized, rude, or to posers or strivers who try to cram as many parties as possible into a single evening.
Hee. I usually try to arrive as early as I can, but not so early that I’m in the hosts’ way while they prepare. If I know the host well, I’ll ask if they need prep help and show up when they need it, so they can have everything ready and be able to have fun and socialize at their own event instead of having to worry constantly about running it.