I already have iOS 6 on both my iPhone 4S and iPad 3. Lifehacker had an article up last week with the GM builds so I installed them. I did it last year and had no problems so I figured I'd do it again.
I've been really enjoying the Do Not Disturb feature at night, as it allows me to keep my ringer on just in case someone needs me. I used the new reject-a-call-and-text-back-immediately feature last night while at work. Pretty handy actually. Panorama looks cool, but with school I haven't had a chance to go out somewhere good and try it yet. Hopefully it works as well as Microsoft's panorama app.
I haven't had a chance to play around with navigation in the new Maps yet, as my new to me car has navigation built in, making my iPhone's nav not really needed. Maybe I'll put the two up against each other. See who is better: older Acura or brand new iPhone. Which do you think will be?
All in all, iOS 6 is a good improvement on iOS 5. Nothing ground breaking for me personally, but I still really enjoy some of the smaller features.