On the D3100, D5100, and D7000, Nikon placed a rather low video recording time limit for a single clip. Currently, it's somewhere in the area of ten or 20 minutes, depending on the model. However, Nikonhacker.com has come up with a crack that will extend this limit to a much more reasonable 25 to 30 minutes. Read after the jump for more info!
Of course, this is not an official Nikon release, so anything you is at your own risk. But it has been tested to work on all three models (the D3100, D5100, and D7000), so there shouldn't be too much to worry about. Simeon Pilgrim has a great bit with download links and directions here. Good luck! And tell us in the comments section how it goes for you!