How does it decide to put something on the homepage? I know it's not only vote count, but what else is taken into account?
The exact process is unknown and has changed much over time. Votes from power users will generally have more weight then votes from non power users (At least it used to be this way) also collectively votes from common friends will have less weight. So 10 Votes from 10 people that are all friends will not have the same weight as 10 votes from 10 random people. Bury's will also hurt the chance of becoming popular. The system also looks at the voting history of users, even if they are not friends if multiple users have a history of voting for the same items it will also lesson the weight of their vote. It also seems that too many votes very quickly together after being posted will also affect it negatively. Comments left will aslo probably help.
It also takes into account the age of votes, and the frequency with which it gets them, so a post that gets 100 votes in an hour will rank higher than a post that gets 100 votes in 5 hours.
There are probably a lot of other factors that go into that aren't known, such as the rumor that users who have gotten to the front page before are favored and more likely to get there again, which could be why the top 100 users control 56% of the front page.