Squidoo's philosophy is that everyone is an expert. They are allowing anyone to have a page on any topic, for free. The system is funded by advertising revenue.
The benefits are all explained on their home page, here: www.squidoo.com
You can showcase your book, add links to it's page at Lulu or wherever, links to your blog and Amazon, say what you want about it, and get feedback too. There are common interest groups you can join, and the system will allow you to create a page about yourself. In addition, there is a lot of cross-linking on the site, which gives you higher ranking on Google and other search engines.
Here is the link to my page, by way of example: www.squidoo.com/choosetolive