http://dovecot.org/releases/1.2/alpha/dovecot-1.2.alpha4.tar.gz http://dovecot.org/releases/1.2/alpha/dovecot-1.2.alpha4.tar.gz.sig
Note that there are significant changes in this release from alpha3 and I haven't tested everything extensively. Be careful. The next release will hopefully be v1.2.beta1 with a feature freeze.
Most importantly shared mailboxes and IMAP ACLs are finally supported. This is mainly thanks to the Kolab people (looks like I forgot your names from NEWS file, the next release will have them).
I'll have to write a wiki page about ACLs, but the main thing you need to know is that if you want shared mailboxes to be LISTable by other users, you'll need to specify acl_dict. If you don't expect many shared mailboxes, a file backend is the easiest, but you could also use SQL or Berkeley DB. With a file backend you could also create per-domain files, which will improve performance if you don't need cross-domain shared mailboxes. You could do this with e.g.:
acl_file = /home/virtual/%d/shared-mailboxes
Also full text searching works now better with virtual mailboxes. Previously the fts would have duplicated the indexes for virtual mailboxes. Now with Solr backend it searches the original mailboxes directly. Although this is still missing some optimizations and also it doesn't check first if mails are missing from the original mailboxes, so it may not find everything. Also this still doesn't work with Squat backend.. Anyway, a bit more code and Dovecot will have fast full text searching from all mailboxes (virtual * mailbox).
I implemented also draft-gulbrandsen-imap-response-codes-04, which adds some [codes] for all IMAP command failures, which should make it possible for clients to figure out more easily what caused the failure. Hopefully the draft won't change much anymore. :)