We have not had time to install 9.1 yet, but as soon as we do we will give you a full report. In the meantime, Apple has this to say:
Mac OS 9.1 Update is designed to support todayis Mac OS 9 customers and ease the transition for tomorrowis Mac OS X customers. The Mac OS 9.1 update delivers additional support for Multiple Users and iTools services, and Sherlock 2 has a new channel, Entertainment, making it easy to find movie reviews or your favorite song.
OS 9.1 is available as a free download for users of OS 9.0 or higher. You can find more information at the Apple web site.