It's a book worth reading if you are trying to market yourself, a service, or a product online. For me it helped to inform the development of my 'online self'. It's so good, in fact, I'm taking the time to give it it's own little post!
The key lessons:
'Content drives action'. This is a phrase the author, David Meerman Scott, uses quite frequently, and rightfully so. In essence, the more words you have on your web site, the more chance someone is going to have of finding you.
Create valuable content. If you write bad content (just a list of key phrases or really gunning for a sale), people won't linger long. If you write valuable, informative content, you will find more people becoming interested in who you are and what you are saying - the result of this will be more interest and trust in your business.
Become involved in your appropriate online community. Find other blogs and forums about your profession or area of interest, comment and start discussions. You will become a valued member of the community and you will be more up to date with any new developments around the world.
Finally some tips and tricks (in no particular order).
Use blog search engines to find specific phrases about you or your company - this will show you what others are saying about you (or if they are talking about you).
Think of specific phrases that someone might use when talking about finding someone to hire for a position that you could fill - search it in twitter then reply to that tweet, it's almost like using someone in your own network to find a job!
For each subject you write about, write the first sentence with key phrases and keep in mind that if it pops up in a google search, this is the extract people will skim over. (That's SEO, not some in depth complex exercise in technology - it's identifying key phrases and using them in an appropriate context).
Overall, this book lead me to re-design my personal web site (several times) and join a graphic design forum (http://www.graphicdesignforum.com/forum/showthread.php?t=77738) in which I try to comment or post a new thread once a day. I have also started to post anything of value that I can think of onto my blog, including sections of this book, you might even be reading this on my blog! If you are unsure whither these things work - keep in mind you are reading this which means it is working for me, right now!