Microsoft has unveiled its new project code-named Velocity {via}, which is a .NET version of memcached for the Microsoft orbit. It's not at this point baked into the OS or IIS, but it's a start.
It's got some additional features that go beyond memcached. One of the great things about memcached is its simplicity and limited feature set. It doesn't worry about security and it's essentially a glorified hashtable. For example, it offers named cache stores, regions within those caches, object searching, and different concurrency models. I can envision a lot that such functionality would get me if I were to replace memcached with it.
But I'm most curious as to the future of this project and its official position. If it's going to become a supported technology and/or officially bundled, then I'd be willing to invest the effort in switching. But if it's a one-off and never gets much attention, then I'd rather stick with the power horse that is memcached. There's plenty of hope listed in their future feature list. I'm subscribed to the blog and I will be following this project closely.