Today I've released +DAViCal 1.0.2, a paltry collection of small bugfixes and minor enhancements. The most significant changes are to fix a bug in the way external authentication loaded permissions, and to add the ability to upload a file of VCARD into an addressbook.
I believe this fixes almost all of the notable issues at present, so I've uploaded this to Debian as well as in my own repository.
Full release notes are on the wiki.