Why does everyone keep saying 2012? Historically, Macbooks have been refreshed, on average, every 10 months. Thus, the next refresh would occur at the end of this year, December '11, in time for the holidays, perhaps. Although, for some strange reason, Apple has liked to wait for the doldrums of January to debut or announce things.
I know there's a growing contingent on this forum, that want Apple do nothing other than abandon the optical drive and put that space to good use. Their points are tenable. However, I'd be very, very, very surprised if Apple cast aside the optical drive for this next refresh. To the less computer savvy, its absence would be a big deal breaker. "How am I gonna install software?" "How am I gonna burn a CD?" So expect the optical drive to be with us for a while.
The likely updates for late 2011 (or early 2012) are an increase in screen resolution, especially in the 13" model, and Ivy Bridge processors.