From the infamous Privatemusings arbitration case:
The use of sockpuppet accounts, while not generally forbidden, is discouraged. Abuse of sockpuppet accounts, such as using them to evade blocks, bans, and user accountability—and especially to make personal attacks or reverts, or vandalize—is prohibited. Sockpuppet accounts are not to be used in discussions internal to the project, such as policy debates.
Passed 8 to 0 at 12:12, 2 December 2007 (UTC)
From the userpage of Antiselfpromotion:
My objective with this ID is to help keep Wikipedia from becoming the apparatus of self-aggrandizement, marketing, fraud and other kinds of dishonesty. Wikipedia is becoming more trusted and global than ever but its neutrality and its respect rely on the honesty and good will of editors.
I mostly implement this ID's objective by researching and participating in AfD debates. Maybe that sounds too destructive but it is just one side of the coin. I am a longtime editor under another ID, but in my work I have noticed that many people who use Wikipedia to promote themselves get very upset and sometimes retaliatory and abusive when their pages are nominated for deletion. I have decided to do my AfD work under a new account for that reason.
If I thought Antiselfpromotion was actually violating policy as I understand it, I would report it to the appropriate noticeboard. I actually think the Arbitration Committee principle in the Privatemusings case is ill-advised, and this user's contributions, which are indeed almost exclusively on AFDs, perfectly illustrate why this sort of sockpuppetry is okay.