I used to rent games all the time, by the armload (Not literally, but I did rent alot at once) Now, I only rent games whenever I see a title that catches my eye (usually a Star Wars, Fighting, or WWII game)
Since it's rather expensive to rent ($7 for a week? I wish it would go back to $3 or $4 dollars) I buy most of my games, because in the long run, it's cheaper. Plus, if you don't like the game you could just return it or sell it.