Read this before you update to 10.5.6
 

10.5.6 looks to be mostly a service-pack of bug and stability fixes but nonetheless, there will be people who will run the update and find that something critical doesn't work anymore. Avoid this potential pitfall and follow the sticky listed above, "How to Update your OS and Apps...". It will take far less time to do this than having to reinstall your entire workstation again.

And be sure to follow the golden rule: If you're in the middle of a project DON'T UPDATE ANYTHING. Finish and output your final work first, then follow the guide in the sticky so you don't create a major hassle for yourself.

Cheers.