Interestingly, a few years ago — before LiveJournal's takeover by SixApart.com — the management released a "Social Contract" stating that LiveJournal would remain advertisement-free. Unfortunately it is impossible to link to this page at LiveJournal, as it has been silently deleted. However, we can read a copy of the document on the Internet Archive.
The user outcry has so far been limited to those who actively watch the lj_biz community. However, users are employing their own "viral marketing" techniques to spread the word across the user base. Many are worried about a MySpace-like descent into user-targeted advertising.
All this comes after the user base resisted introduction of advertising-supported user accounts, which swapped paying for extra features for seeing "targeted" banner adverts on the site.
These events raise prickly issue of user rights on such websites, and the validity of "user contracts" that can be changed at will by the provider with no subsequent compensation to affected users.