Consider waiting to install OSX 10.5.3 if you work on image files from one system (i.e. a JBOD farm) on another system connected via Ethernet. The files corrupt when Saving back to the drive connected to the main server computer. This is a documented issue (search the Net to read more) that needs a fix by Adobe or Apple.
Note that you can work on an image all day saving with no indication there is a problem. Only when you close the file and try to re-open it do you see the Corrupt Image message. By then, it's too late, you lose all that work.
There is a workaround, so you're not dead in the water with 10.5.3. Use "SaveAs" rather than Save.