Downhill is horrible on fixed. There's a pretty steep one on my daily commute with a bigger road at the bottom, if it wasn't for my front brake I'd be toast.
Hills are a good way to get fit when riding fixed- up hills that is! I agree with tbc on the downhills! I've had a couple scary downhill moments- when it takes you for a ride... good job I've got a front brake too.
you wont get up many hills in north wales on 42 x 19 unless you are called Alberto 'el pistorello' Contador
Fixed gear totally un-suitable for around here unless you have a double fixed hub and keep changing your rear wheel over..