db2diag -l Error,Warning -fmt "%ts %level %db"
This would only print the timestamp, the "error" level, and, if it was for a specific database, the database name.
2010-02-05-13.05.51.947000 Warning
2010-02-05-13.05.52.449000 Error PUREDB
2010-02-05-13.05.52.449000 Error PUREDB
2010-02-05-14.10.24.619000 Warning
The output is much quicker to digest than the diagnostic itself. And I could also use the output as input for some other scripts. Have you used db2diag in the past?