I attended a great presentation about Omeka by Amanda French sometime in the morning on the first day of ThatCamp Jersey Shore. I have become interested in Omeka recently, as I had been considering moving the flyer archive over to it. After hearing Amanda speak, I have decided not to move it, but i think there are plenty of great uses for Omeka.

Omeka was built for use by museums and archives
Omeka.org is server side software. Must have a server to publish on your own.
Dreamhost does one click installs of Omeka.
Omeka.net is a hosted version similar to wordpress.com
There is a lot of potential for metadata (Dublin Core) in Omeka. Standards are set by archivists and librarians.
The interface for Omeka is similar to WordPress. Adding an item is really easy.
A big downside I found was items only being in one collection at a time. Tagging may work better for that ala WordPress.
Plugins for adding an item to multiple collections may be coming soon.
Archives about Hurricane Katrina run on Omeka.
TEI looks very interesting. For example, in one of Washington’s letters would add “Martha Washington” to words “my wife.”