SQL Server Books Online (BOL) has improved dramatically in SQL Server 2005. I'm not necassarily talking about the content (though that IS better I feel), I'm talking about the ability to provide feedback about the articles. What's great is that if you use the 'Send Feedback' link in BOL your comments get emailed straight to the person that wrote the article.
I have taken advantage of this many times and its very gratifying to see the amendments that you have suggested in the next release of BOL. In other words, BOL is an ever-evolving and ever-improving beast and it is worth making sure you always have the latest copy on your machine. They are not released simultaneously with service packs either, they are more frequent than that. As I write the latest copy was released in July 2006 and is downloadable from here: http://www.microsoft.com/technet/prodtechnol/sql/2005/downloads/books.mspx
Its very simple to check which version of BOL you have installed. Take a look at the title bar of BOL, if you have the following:
then you are running the RTM version of BOL - i.e. the version that was released alongside the product in November 2005. If you have the latest version then the title bar will look like this:
So what are you waiting for? Get downloading!
-Jamie