Microformats are a great idea. They allow the embedding of parsable, semantic data (like contact information and event details) into regular pages. With the right plug-in, that information can be saved directly to your calendar program or address book. Like Microformats, a portion of web accessibility is about making pages more machine-readable, and by doing so, making them more usable to human beings.
Most of the time, Microformats and the principles of accessibility coexist harmoniously.