We actually already have Categories aka Tags and a Tag Cloud in the blog. The plan on the road map is to make a more general tagging system that can be used by any feature not just the blog, but when it is ready we will replace the current blog tagging with the new system.
I've been working on SqlCe support in mojoPortal and already have it working for the core but haven't yet implemented it for the mojoPortal.Features projects. You can expect me to blog about it soon.
Best,
Joe