I noticed that when downloading a file it kept connecting to users but couldn't download of them. I checked dat view and I had 150 names stored and Kazaa was going through this list and it occured to me that these ip# could have expired due to the isp rotating them or they are no longer connected to the particular supernode. I used they icon of the eye in dat view and deleted most of the sources after making a backup of the original dat file and then started kazaa and searched for the file. This gave me lots of up to date sources to download from and speed up my download.
Hope this helps
Also found that if you type in the ip# of a source that was fast before in kazupernodes it can give you there new supernode just connect to them and this may get you back to that fast source, although this is not guarented but worth a try for rare files