/Developer/Applications/Utilities/CrashReporterPrefs.app can make crash reports much more useful. It will show crash-reports for background processes, and stack-trace in the notification dialog.
Crash report-files are stored in ~/Library/Logs/CrashReporter/
Unfortunately, crash reports are not sent back to third-party developers, even when you send them to Apple.
EDITED TO ADD: This still works in Snow Leopard (Mac OS X 10.5.6)