i got the same problem (see my thread "internet performance irregular since installing limewire").

it is not that limewire is using all my bandwidth - limewire also only downloads at 1-2 kbps. after it is running for approximately 20 minutes, all bandwidth just disappears, going from 25kbps down to 1-6 kbps.

you can test your general speed at speedsuite.net, the test is not being influenced by any other programs currently using the connection.

this appears to be bug in limewire.... some feedback from the developers would be appreciated?