Here's what I've learned lately.
Get rid of old downloads, anything waiting on sources etc...
My connection speeds up when I do that.
Anything running in the background seems to slow me down as well as items in the system tray. I use the task manager to monitor my system.
When I use LimeWire, I don't do ANYTHING else.
I found out my port assignment was off and when I changed it and did all the other stuff, it took off turbocharged.
Also, when you have a ton of stuff waiting, it seems to affect it.