There's some evidence that demand for Treasury debt might be waning. That makes sense on a number of levels: Deficits look bad and so the risk of default -- though quite small -- inevitably inches upwards. There are signals that other markets are stabilizing and their products may once again be worth investing in -- and may even be extremely good deals. International investors aren't quite so terrified and so aren't essentially trying to hide their money beneath the United States' mattress.
We're probably at the beginning of the period when it becomes more expensive for the government to borrow. Since the recession began, it's been uncommonly cheap. As the recession ends, it'll normalize. So if the government is planning to borrow a whole bunch of money in the near future, it might be a good idea to lock it in now, while 30-year rates are low, rather than later, when they rise again.