I am running 1X9 on my Peugeot P8. Love it. I can easily get over 30 mph on the 42/12. I see no reason for a bigger gear than that here in Boise for a commuter. I have never dropped a chain but I do have a problem getting the friction shifting to stay dead on. I get some ghost shifting (especially when I sprint). But I think that is more a function of the shifter.

I think Ontheroadid runs a 1X9 here in Boise as well. Most East-West Boise area commuters only have a 100 foot bench to climb (if they have to deal with that).