I installed the Firefox Extension Greasemonkey about a month or two ago. After using it for a few days, I decided to turn it off, mainly because some of the scripts were just annoying and I didn't have the time to deal with it.
I finally turned the Extension back on and I added some of the Slashdot scripts. Although I knew Greasemonkey really had the potential to be great, it wasn't until I used it for the past couple of days that I realized how great it is.
Am I late to the party? Yes. But, hey, at least I finally realized what I was missing.