The December CTP of Microsoft's Parallel extensions has recently been released. Some info from the download page:
Parallel Extensions to the .NET Framework is a managed programming model for data parallelism, task parallelism, and coordination on parallel hardware unified by a common work scheduler. Parallel Extensions makes it easier for developers to write programs that scale to take advantage of parallel hardware by providing improved performance as the numbers of cores and processors increase without having to deal with many of the complexities of today’s concurrent programming models.
Basically a set of extensions designed to help utilise all those multiple core processors out there. Looks like it's pretty easy to throw some basic multi core support into your applications - there really is no excuse to not take a look if you're doing anything which is processor intensive.
Link: Microsoft Parallel Extensions to .NET Framework 3.5, December 2007 Community Technology Preview