I've done some work with WikiTalk on my Intranet site (http://www.gearboxsoftware.com), and I am hoping to contribute much of it back here.

Some things that have made it so far:

• 2005-08-27 -- ConciseTimeSpanFormat along with OrdinalString which does GMail-like "2 minutes ago" handling singular and plural correctly. Note that this would be probably better implemented as a Plugin but it was quick and easy to whip this up, and I suspect that others may find it useful.
• 2005-10-12 -- RFE 1052389 supporting per-namespace StyleSheet override. This was submitted to flexwiki-users email list for comment.

Some things I am working on:

• An interim security solution that allows a small number of pages to be secured via NTFS file permissions. This solution is not suitable for large-scale security as it has to bypass the cache, but it works reasonably well for sites that need to secure a very small number of infrequently used topics. Contact me directly if you are interested in this. I can provide patches, but I can't provide any official support...
• A simple WikiTalk-based preferences system that ties into a custom border set so that users can add links to the borders easily.
• Enhancing WikiTalk by adding regular expression support, and some helper methods to various classes
• * This is currently completed in a beta state. I am preparing to package things up as a ChangePacket very soon.
• Vastly enhanced border set suitable for Intranet usage. The border set moves around several of the UI elements and enhances the usability of the page.