Spending some of my time off exploring microdata and html5 more in depth. If the semantic web is going to finally gain wide adoption microdata is going to be the catalyst. Unfortunately as easy as it is, it still involves a some effort to add microdata to your code. Still it is a million times easier than XML or other semantic formats.
Unfortunately, I think performance will still be an issue in actual implementations. Microdata is still fairly verbose and also referencing the scope/schema from a third party server may be a problem for some high traffic servers. Adding microdata to your mark-up can easily double or triple the size and there is always the latency issue of referencing a third party server.
These were the sources I was reviewing;