OSX 10.7.3 upgrade problem - installation hangs before reboot

My system: late 2010 MBP 15" i7 2.66 GHz 8 GB RAM OsX 10.7.2 with filevault 2 enabled.

I recently tried to install the upgrade for Lion 7.3 from Lion 7.2 using the Lion 10.7.3 Client Combo DMG installer d/l from Apple's web site. (I thought this would be safer than the Software Update app). I had closed all other applications. The install went fine until it froze at "moving files into place" and reported 1 minute to go but without further progress for an hour. I could not exit or force quit the installer and so had to force a shut down and because the OS was now corrupt I couldn't boot. I had to use recovery to restore my system from a time machine backup (thankfully this worked or I really would have been SOL).

Last July the upgrade from Snow Leopard to Lion went without a hitch, but similar less catastrophic problem occurred several months ago with an upgdate to iphoto using the automatic software update (stuck again on moving files into place). iphoto was corrupted but I was able to repair it using the dmg installer for the update.

In between these two events I've done several normal update installs for both Apple and non-Apple software without problems.

Have you encountered this problem before? What can I do to avoid this catastrophic problem with future upgrades to Lion (I'm still stuck at version 7.2)?

I have heard conflicting things about the usefulness of fixing permissions, clearing caches, installing in safe boot mode. I don't routinely do any of these things (I thought the thing with iPhoto was just a one-off). I also have Inetgo antivirus installed (because my clients require antivirus software not because I think I need it) - don't know if that interferes as antivirus software does in Windows.

Any advice would be very much appreciated. I'm planning on sticking to 10.7.2 for the forseeable future, but I need to be able to install updates to both the OS and key apps to keep my system functional in the long run, and I depend on this mac for my business.