This is a recommended upgrade with a focus on stability and reliability.
Release notes are on the wiki at http://wiki.davical.org/w/Release_Notes/0.9.9.4.
Most of the changes are subtle: fixes to small bugs or adjustments to correctness in respect to standards. In particular there were some errors in handling of various requests for addressbook data, and the support for WebDAV synchronisation is updated to draft -04 of the specification.
One notable addition is the new '/feed.php/username/calendar/' URL which will provide an Atom feed of the events added to a calendar. This is pretty experimental at present, but any problems with it won't affect the rest of DAViCal so I felt it safe to include in a stable release series.
I've also created a DAViCal Announce mailing list which in the future will be the primary place that notifications like this are sent to, so those of you who are subscribed here but really only want to see announcements should subscribe to that list.
In a few weeks time (well, when I remember, I guess :-) I want to move the DAViCal General mailing list to a lists.davical.org mailing list. As of today I've moved the DAViCal developers mailing list there already (pretty easy since it did not involve moving servers) but the old address for that one will continue to work indefinitely.
Also, as of yesterday, the sourceforge.net project name for DAViCal finally got changed, so DAViCal is now at http://sourceforge.net/projects/davical - yay!
At the end of January I will be presenting about Calendaring and Free Software at Linux.Conf.AU 2011 in Brisbane - I hope you've all got your tickets already, because there isn't much time left now :-)