What it does is an effective 'shuffle' through the internet, like the shuffle on an ipod except with sites instead of songs. Once you sign up (FREE!) you can tick all of your interests and it randomly generates a page. So next time you're bored, you can just go on stumble and hey! You suddenly have something new to read/ look at :D and the best thing about it is that it gets better each time you use it and more honed to your tastes.
So to conclude, here's something random I've found on stumble recently - enjoy!
