I have heard that it is okay to let it go over that much, but it kind of depends on who you talk to or what you read. I typically change my oil about that often and so far I haven't had any problems.
I always keep checking the oil once a week to see what the color is. When it gets too dark for my taste, I change it. It's usually around the 2,000 mile mark.
I usually change mine between 3,000 and 5,000. I think Spokane has the right idea about checking the color. If you don't feel like checking it every week, every other week would be fine.
How hard are you driving the car? I know with the new one we got the did an extend for all vehicles in our house so even if we take a car we did not buy with the place (family owned in our area), they still change all oil for ten bucks. If you can snag a deal like that there really is no excuse to go over the recommended time.