How many times have you read it? Did you start with the book and move to the website? (Anecdotally: I enjoyed until the half of it reading it while commuting but lately I've found that you can read them online (for free?!) And also have comments to every essay in part.(which I found insightful) should one start again but read it through LessWrong and the comments?
I've read it 3 times and think it's the best book ever. What a coincidence that I'm someone who is currently spending time on LessWrong.com and becoming part of your sample of answers eh?
I read the website before the book existed. Actually, I argued that it should be turned into a book, because books in general have higher status than websites. Then I read the book, and translated it to Slovak language.
My opinion on reading the comments is... they are interesting, but the added value per minute spent is significantly lower than reading the book. (Some of the comments are awesome, but most are not, and there is a lot of them.) Thus, if you have anything useful to do, reading the comments after you have read the book is probably a waste of time. (Perhaps, if you have specific questions or objections to specific chapters, you should only read the comments in those chapters.)
Your time would probably be better spent reading high-karma articles which are not part of the book (is there a way to see the highest-karma articles? if not, look here), and... you know, going outside and actually doing things.
Read a few of the sequences. Then read the book. Then read all the sequences.
I found the book very good.
I read most of the Sequences when they came out, but haven't tried re-reading them in the book.
I am currently reading it, currently in the Quantum Physics sequence. I read it all here on LessWrong, I did not buy or read the book version. I sometimes skim through the comments a bit, but sadly, the threads have been unraveled a bit and it is hard to follow a conversation. I don't remember any specific occasion where the comments enlightened me in a new way, though they are sometimes interesting. I doubt it is necessary to read them, though.
I've read the Sequences and I'm almost finished with listening to the audiobook version of the book as well. (On account of how big they are, I didn't know I had read them all, until I listened to it and I said, wait, I've heard all of this. (And my responses to surveys reflected this.))