Trying to work 100+ downloads is probably not normal for most OS X users, but depends on which OS X and machine. I'm assuming you are using LW 4.8.1

You can get the relevant details from LW's About box, or the Preference's Bug Reports->View Example.

Activity Monitor (in your Applications/Utilities Folder) will give more info. Sounds like LW's Virtual Memory use is getting high (above 1 GB), disk space getting low (<2), and then everything else slows down while OS X tries to swap memory--beach ball time.

Shutting down your machine for a few minutes can help; working with fewer downloads would be better.