There is a possibility that your isps are truing to curb your use of p2p and are strangling your upload bandwidth.
Otherwise, it really depends who is trying to upload. I have some who try to upload a file for hours, with little success. For all I know they are on a modem trying to download 20 files at once. Most hosts seem to get perfectly good speeds for uploads off me.
If you can download at 100kb/s that is great, but remember you may be getting a file from multiple sources, but if you are connected to a slower computer, the speed is going to be governed by the slower machine and it's connection.
Also: another host may be uploading from several hosts, including you and the upload from you may be apparently switching off ond on, but the file is downloading smoothly at the other end.
If you see Upload limit reached, I would not worry about it. For some hosts who upload off me it happens to every single file. The transfer interrupted message on the other hand might be an indication of a problem. It is on these occasions I wish the chat feature actually worked. We could then perhaps find what the problem was and sort it.
The Faq and user guide are available at
http://www.limewire.com/english/content/support.shtml
I'm not an expert on the technical workings of the network, but I hope I have given you some reasonably useful food for thought.