First, the uploader code has not really been changed between 2.7 and 2.8. It's almost impossible that you see a reduced performance with uploads.

Uploads are possible, but you will not see many if you are sharing files that are very common on gnutella or if you are sharing files nobody wants. - Besides, LimeWire removes uploads from the upload tab if they are completed or if they fail.

As far as downloads are concerned. They are might seem a little slower indeed. LimeWire has started downloading in 100K chunks from clients with http1.1 support. When downloading from clients with weak http1.1 implementations you will see a reduced download speed indeed. That should become better over time, when more people update.