Yes, I'm currently doing some consulting on a lotus notes application and the help contents in the Domino Designer IDE has a lot of useful documentation.
And note that there's a feedback option in every entry in Designer Help -- if something is unclear or misleading, you can point it out and/or suggest a fix. Lotus does pay attention to the Help feedback, and needed fixes are usually incorporated into the next point release. And since the Help file is just another NSF, you can edit your own useful changes, notes and examples into your own copy (or the copy that's usually installed on the server for the edification of others).