About the announcement of BB returning in 2011 not made. There are speculations of the possible reasons. One of them being, that this indeed was the last season. Then again, some people think that they wouldn't have built a completely new house for just one season. The possibilities include a celebrity-edition for next year and also the confusion about the producers.
I guess we'll find out around February-March the latest. If they're making a regular season, it most likely would still be in autumn. And that being the case, the auditions would start in April. The latest.