I've been using LW for a few months, and at first it worked reasonably well. I subscribed to Pro, and it was still OK.Then it started quitting partway thru a download. It gets to 5%, 12%, maybe even 30%--then sits there forever. I upgraded to 3.5.8, but more of the same. Does this happen to others? And why?

Yep it does happen to others. There are two reasons for this.
1) the remote host may disconnect from the network
2) the remote host is firewalled and after the direct connection is lost (which happens far to often due to a little bug in LimeWire's upload code) a push attempt fails.

Thanks for the response, trap. I can't help wondering though how anyone can continue looking for downloads on LW if this is the way it is. I used to be able to get a 100% download at least half of the time. Now it's maybe one or two in a hundred. Are there that many firewalls?

It always depends on what you are trying to download. If you are trying to download some piano sonata that is almost unique on the network your chances to complete the download are far lower than if you were trying to download some Robbie Williams song.

Personally, I find LimeWire quite reliable and almost on par with Fasttrack. I can't tell why you are so unlucky, my downloads tend to complete at least in 50% of all cases once the download started.

Eureka! I just discovered what was wrong. The signal coming through my cable connection had weakened. It was slowing things down generally, but for some reason affecting LW most dramatically. The number of hits was shortened, and--as noted above--it was nearly impossible to complete a download. After a service call by the cable company it's back on track. Just sorry it took me so long to figure it out.