Since the introduction of SQL Server 2005, there is a simple lightweight trace that is left running by default on every SQL Server. This provides some very valuable information for the DBA about the running server, but it isn't well-documented. Feodor Georgiev reveals many of the secrets of this facility and shows how to get reports from it.
I would like the option on some servers of having a profiler trace running 24x7 in the background. I could then access and read these trace files to investigate issues after the fact - much like the default trace that came out with SQL 2005.