Rated 5 out of 5 stars
This does one thing beautifully - it BLOCKS sites that you don't want to be bothered with. Sometimes - even though I'm pretty safe with ABP, et al., something manages to get through. All you have to do is add the site to your BLACKLIST, and...gone (it also has whitelist, if needed). My rule is simple; an add-on should DO what it says it'll do, and do it well (and as easy as possible). BlockSite does so wonderfully.
Some people believe this'll block sites from their kids and suck - no. It's not like Cybersitter, etc - It's for YOUR use, so you don't get BOTHERED.