Cough cough ljbook.com cough. Which, incidentally, exists in the context of online communities and social networking websites. It's named 'LJBook' because it does what it says on the tin - it makes a book from a LiveJournal. What's more, they've been around for sufficiently long, well over six years from the looks of it, that they slightly pre-date Facebook.
That 'trademark' has been comprehensively diluted prior to Facebook even registering it, primarily due to the fact that it's such an obvious name that a whole lot of other people thought of it first. According to TESS (http://tess2.uspto.gov/) their trademark was filed in Feb 24, 2005.
IC 038. US 100 101 104. G & S: providing online chat rooms for registered users for transmission of messages concerning collegiate life, classifieds, virtual community and social networking. FIRST USE: 20041116. FIRST USE IN COMMERCE: 20041116
Standard Characters Claimed
Mark Drawing Code (4) STANDARD CHARACTER MARK
Serial Number 78574730
Filing Date February 24, 2005
Perhaps the lawyers ought to have gone after HighPoint Technologies instead, who registered 'my+facebook' as 'external storage hard drives for sharing, accessing and downloading media through the Internet by using propriety hardware and software. The external storage hard drives allow users to upload and share media, play music and videos in addition to viewing photo slideshows by utilizing a software interface from a group of invited guest and users.'
As for other people to go after, TESS suggests the following:
AMBook - online files
PlanBook - lesson planning for educators, with sharing of plans via PlanBookConnect
MOBook - online travel planning
PartyBook - business networking
D VIdeobook - educational services
Gracebook - internet portal for social communications, the fiends
Placebook - geolocation software
TheLookBook - fashion online networking
BookBrowse - online book review centre from the 90s.
LiveYearBook
MarketBook
StudioBook
ShagBook (dates from 2006, this one)
Mobibook
Smilebook
Fieldbook
Whichbook
Sportsbook
Genebook
Sharedbook
Dealbook - online news, shared databases
and over eleven thousand others, which is enough to make you wonder whether some-short-word-plus the suffix 'book' is a distinctive enough trademark. Some guys who I wish Facebook would sue, just because there are some good headline opportunities there:
LameBook - which reposts everything lame and funny about Facebook. A full-time job, especially when they're acting out like this.
Comparing this one to the Victor's Little Secret case, concluded earlier this year, would seem to suggest that Facebook have a better chance against ShagBook. It's marketed to a fairly similar audience, but comes with added value sexual overtones, and is therefore likely to tarnish the mark. IANAL, obviously.