According to the WordPress codex, my Advanced TinyMCE Editor has been tested and found compatible with WordPress v. 2.3. (About 160 total plug-ins have been so verified.)
This new WP version adds enhanced support for tagging, among others (see Aaron Brazell’s 10 things you should know about this release).
I will be doing my own testing when a stable release is issued, but this is good news for this popular plug-in. You may get version 0.5 of Advanced TinyMCE from here.