Why is steam downloading so slow?

yesterday i downloaded saints row 2 at almost 1mb per second which downloaded the 12 gbs pretty quick while i went out, today i went to download mw2 single player and multiplayer again from steam and it's so slow at 100kb/s, team fortress 2...don't even talk about that, its at 1.5 kb/s...nice aye? what could i do to fix this stupid steam issue?