0.91 is an improvement over 0.90 for sure. But we don't believe that it's a critical upgrade.
I'm eating lunch with altoz right now and he also says he's had problems with 0.90 that required him to delete the .armory directory.
I think you've got a lot of users who having problem but are just living with them instead of reporting them.
i have had zero problems with 0.90 (zero crashes) and that's after putting it thru heavy testing.
of course, my laptop has 16GB RAM with a huge HD in linux.