I've started to test iTunes 11 with Remote Buddy right after Apple released the update last Thursday. While most basic commands continue to work fine, more complex tasks unfortunately don't. So far, I've identified these issues in iTunes 11:

1. Scripting support for shuffle and song repeat is broken (via Doug Adams)
2. The play command behaves differently. In previous versions, you could simply tell iTunes to start playback of a track in a playlist and iTunes would play this track - and then the rest of the playlist. In iTunes 11, it will only play a single track.
3. The reveal command behaves differently based on whether or not the user opts to show the sidebar. Also, iTunes 11 will loose a selection made this way when you show and hide the sidebar.
4. The Remote Speakers are now managed in a popup. This popup is not locatable via UI scripting: the popup provides the iTunes window as its parent, the iTunes window, however, doesn't provide the popup as its child.
5. Since the sidebar is now optional, using its shared library entries to build a connection to a remote iTunes library requires the sidebar to be visible. At the same time, iTunes doesn't provide any status information as to whether the sidebar is currently visible or not.

The impact, especially of point 2, on using Remote Buddy's built-in music library browser to access and play your content has been pretty deep.

Luckily, I found ways to work around most issues. An updated iTunes Behaviour for Remote Buddy 1.22.1 is now available via the built-in Online Updater. What remains broken due to bugs in iTunes is shuffle, repeat and controlling remote speakers. I hope to implement work arounds for these in a future release.

[Update 2012-12-18] A new compatibility update for iTunes 11.0.1 is now available via the Online Updater.