A number of cosmetic issues, UI tracebacks and outright bugs (such as 32 bit plugins not working) have been addressed since 9.1 was released. A few features that were known to be broken, such as AIO in Samba3 or IPv6 in plugin jails, were also disabled to avoid people shooting their feet off.
Finally, a number of important ZFS stability fixes were also picked up from the TrueOS repo during the creation of 9.1.1-RELEASE.
Thank you for all your participation and assistance during the 9.1.1 BETA and Release Candidate process. This release benefited significantly from your suggestions and bug reports!