Here is a handy blog post by Brian Bischoff on the SAP network. It provides a map of CR version numbers to their associated service packs. So now you can see from the version number (in help about) how far you are on the service pack series for your version. This only applies to Versions XI, XIr2, and 2008 (also known as versions 11, 11.5 and 12).
And, thanks to Jamey Becker of Answers on Demand, for pointing out this post to me.