My iMac with Leopard 10.5.4 has actually been acting really weird lately. It seems to be getting slower and slower and there's been lots of keyboard and mouse delay. Even my non-technical wife has commented that "the computer is slower".
I'm been thinking about backing up all my data and doing a total fresh reinstallation.
Here's hoping 10.5.5 makes things go back to normal.
And I thought it was because I was using my macbook more, with multiple apps running, and doing video...