Thanks to Egidijus' work in GSoC, we have updated Sparkle (updater for MacOSX) to the latest version. Updates are now signed (from the next build, i.e. 1988 and above), thus improving the security of the updates.
Even though updates from build 1988 will be signed, people that have a build < 1988 and that try to update to a version >= 1988 should be able to do it without problems (checks on the package signature are only performed from build 1988).
Also, update checks happen only on the second and subsequent runs of the application (this behaviour can be changed, but such behaviour avoids to annoy new users with updates on the very first startup).
Egidijus, I've acked your work on growl and sparkle on our website. I've also closed issues #587 (growl) and #597 (sparkle). Once again, thanks for your great work!