Another, more selective way of doing this may be to disconnect your worst nodes.

Check your connected nodes on Statistics, especially the Distribution tab. When nothing happens for a while, I browse through my list of connected nodes and removes those with few friends and small libraries. When new nodes have popped up, I try a Re-Search again.

BUT: Usually I just wait. I have seen files starting to download again after a week or two, and I don't expect 3 weeks is a limit either. The problem is when you have 10 files at 80-95%... The partial files start to take up so much space on your hard drive that when another (new) file download kicks in, your HD may be full...