It might be due to your ISP starting to shape your bandwidth. Who is your ISP (internet service provider)?

Try downlding a magnet link & tell us what type of speeds you get: http://www.magnetmix.com/video.shtml

Speeds normally depend upon your sources, so if the fastest source you were downlding from is offline that might leave you with dialup users or the person with the fast speed is suddenly sharing with many more people thus their upload offering is much less.