I've been using the Firefox plug-in for Stumble Upon for a about a week now.
I wasn't expecting to like it much and maybe that is why I really like it.
If you aren't familiar with StumbleUpon.com, it's a website that shows you web sites you might not know about but might be interested in. This is all based on your preferences and your rankings of the sites it show you.
It showed me some site I like, such as xkcd.com, gimp, audacity, and open office.
But it has shown me lots of site I never knew about. Most of these are Java, Open Source, Physics, Atheist, Native American, Motorcycle, and joke related.
I believe they throw in some random pages just to see what you think.
To see my favorites go here .
Now instead of playing solitaire on my pc, I've been stumbling through the web finding some pretty cool sites. I especially like this one.