You've probably seen Brian Moran's commentary on the value of the SQL Server Books On-Line (BOL) in one of his monthly SQL Server Update e-newsletters. And I couldn't agree more. The BOL are probably one of the single most important tools in your tool kit as a SQL Server DBA or Developer.
Here's an example of why it's so important to keep up to date. The SQL Server 2005 BOL clearly notes in the December refresh (we now have a July 2006 refresh, fyi) that SQL Server 2005 reports the duration of trace events in microseconds (one millionth of a second) while CPU time is measured to the millisecond (one thousandth of a second). In contract, SQL Server 2000 reported both in milliseconds. You might have some scripts break if you don't know this important fact!
Furthermore, in SQL Server 2005, Profiler displays the Duration column in milliseconds by default but saves traces with a Duration column value in microseconds. How do you like them apples?
You can read more about this topic in the BOL Dec 2005 release under the heading of A note about this was added in the BOL 2005 December refresh, in the entry entitled "Viewing and Analyzing Traces with SQL Server Profiler".
Hope this helps,
-Kev
