Think of it as electronic scrap booking. Each lens is made up of modules which are provided for you to add a host of different types of content ranging from your own text, amazon book recommendations, wikipedia content, blog feeds and a whole host of others.
I joined Squidoo some 18 months ago and built two lenses, which sort of lay fallow until the other month. I averaged about 20 visitors a month. I now have over 30 lenses and I'm averaging 170 visitors a week and growing.
There is also a vibrant Squidoo community and ways to cross link to Facebook, Stumble, Digg and so on.
I've really seen significant changes in the visitors to my portfolio after thinking for some time that I'd been a bit gullible in joining. My current top lenses are:
How To Become An Air Guitar Expert
The Border Reivers an ancestry resource about the unique clans that lived on the English and Scottish borders
For a quick preview of my lenses you can see them here too My Squidoo Lens