What did you change right before the problem started? Upgrade to Leopard, software update of Leopard, etc.? Having no extra information my first guess would be an incompatibility of the bundle with Leopard Mail or the 10.5.2 Mail. First thing I do when running into issues with software with addons is remove the addons and see if the problem persists, which is my suggestion to you. Uninstall the DayLite bundle, restart your machine and see if Mail regains its stability. My money is on it not crashing anymore.
That being said, I see in the crash reports that SyncServer is running, which should mean that you are using .Mac. There were issues in the April updates that caused SyncServer issues.
Here is a forum post about issues people had and how they corrected it.