Did you ever solve this?

I'm getting some odd messages in the system log after upgrading to 10.8.3, and a bit of googling suggests that a Safe Boot should get rid of them.

Got to wait for something else to finish before I try it, but reading what Safe Mode does indicates that it might be worth a try for you?

have ignored it as the MBP works . I now have 39.4GB available - really could do with finding out where all my space has gone - but even the thought of booting up in Safe Mode scares the living daylights out of me - what on earth I would do if it threw up any other problems I just don't know - other than panic like mad that is

There are a couple of utilities around that reveal what is using what on your HD.

"Omnidisksweeper" is one that I can think of: https://www.omnigroup.com/products/omnidisksweeper/

Nice program thanks for the link.