Apple has today released the update – all 2.02 GB of it – to bring current Yosemite systems up to version 10.10.3.
This includes its new Photos app, Emoji updates (hardly a key selling point, I would hope), and OS X Yosemite Recovery Update 1.0. There are many security fixes, among which it appears that the Gatekeeper vulnerability which could be exploited in dylib hijacking may have been fixed: I will bring further news in due course.
As I warned before, word from some commercial developers is that their apps may need to be updated, or they will break under 10.10.3, so please check compatibility of your key apps before committing to the update. From the list of security fixes alone, I would think that any apps which do serious things with fonts could be affected by the changes. Reversing back to 10.10.2 is not easy.
My own update here has been a bit of a nightmare. So far I have been gutting my LaunchAgent and LaunchDaemon folders to try to disable any incompatible third-party services etc. but my logs are still filling with copious error messages, and I have had to perform two forced shutdowns already.
One early suspect were the Wacom tablet drivers (once again), which certainly were causing some problems, even though I had only updated them a few days ago.
Another suspect is Apple’s own Server.app, and I wonder if that might be due for an update too.
My advice at the moment is only apply the update if you can spare a few hours to unscramble your Mac afterwards, and know how to. At one stage my Mac would not even perform a Safe restart, which is very worrying.
Latest News early on 9 April:
Apple has released an update to Server which is compatible with 10.10.3 and seems required if you want to run Server under this latest release of OS X. I have now been able to restore all my old LaunchAgents, etc., except for the Wacom Tablet driver (which I still suspect, and it was certainly crashing before I removed it).
I would still advise caution in updating to 10.10.3, but provided that you are not running Server, it looks like it should not be as problematic for you as it was for me. I wish you success.