Last week was Apple's developer conference, WWDC, which I was able to attend. Apple sent me a free pass, which was a great opportunity to meet with Apple's Installer team manager and talk to him about Mac OS X 10.5's use of xar for their new package format. 10.5's use of xar has already been discussed, but apparently xar has provided Apple with huge wins for Leopard. They use xar to create a single file archive, unlike the previous bundles (aka directories full of files), the archive signing brought package signing to 10.5 for free, and the bzip2 compression has provided huge space savings for them on the install media.
Another prominent use of xar lately has been the new rpm5. The new version of RPM will be using xar.
Right before WWDC, xar 1.5 and 1.5.1 were released, which has a TON of new bug fixes, including much better EA archival. This release seems to have shaped up to be the best, most reliable one yet.
While at WWDC, I attended the Spotlight and QuickLook sessions, and wrote a Spotlight plugin for xar, checked in to the repository here. The plugin just sets the creator to xar, the file type to xar, and puts the content listing into the text content field. This basically allows for searching for filenames within an archive, and it returning the archive. A QuickLook plugin is also on the drawing board.