I want to start a site, say vegetablebook, that contains recipes but also has a social element. Should I not do this for fear of being sued?
[1] http://goo.gl/w9SAz
The Teachbook vs Facebook case is still going; Teachbook filed a motion to dismiss on the grounds of venue, Facebook opposed, the matter is still at the alternative dispute resolution (ADR) stage. Facebook declined to have it heard before a magistrate judge, meaning they are probably stalling for time; they might not be confident they will win it, but want to maintain the FUD around anyone using the name for as long as possible.
There is a 9th Circuit precedent that PerfumeBay and Perfume-Bay infringes on eBay's trademarks (http://caselaw.findlaw.com/us-9th-circuit/1050747.html) while "Perfume Bay" does not - largely because searching for perfume e-bay or perfume ebay would bring up their site.
So under that logic, vegetablefacebook would definitely be out, but vegetablebook probably wouldn't be, especially if you could explain what it means without reference to Facebook (e.g. if it had recipes and so was like a book). You might get sued, but I think (or at least hope) you would win if you had the resources to persue the case.