My work laptop came with Norton Security, a sort of firewall, anti-virus software. I have had my work laptop for about 5 months, and it was getting slower and slower, and when I installed Firefox 1.5 on it, it wouldn't load at all. The Task Bar showed explorer.exe was at 99% all the time!
After browsing the web, and seeing too many hits saying, "It's Norton AV," I removed it, since my AV expired on it a few weeks ago.
Yeah. It's like I have a whole new laptop. Stuff I just took for granted, like mapping drives can crash the system... gone!