It's great, I've had no software problems with it, all the featuers work that I've been able to try, not used a few things like the Wi Fi yet. As always what I have and what goes into the shops might not be the same, the one thing that SE have said they were doing is optomising power usage, the battery life could be better but thats an issue they were aware of and in the process of fixing.
With the N91, the phone felt pretty sound, Nokia delayed production because of the specs of new phones just coming out or just announced, there was one or two that were better than Nokia expected I guess. They arn't changing anything hardware wise, but the software on the phone is being given a go over and they're hoping make it more fuctional and allow compatibility woth more formats and devices than it was. The delay may be upto 4 months.