I changed from a 53-39 to a 50-34 compact crank last year for Cheese Country Hell Week held in Richland Center, WI. 8 days, 100+ miles/day, lots of climbing with grades up around 10%. It worked great. The only shortcoming is that I spun out and could not keep up with the tandems on some of the descents - my top gear was 50/12.

One drawback of the compact is that there is less overlap between the small and big ring. This means that you often end up shifting over more cogs whenever you change rings. With STI, this could be a pain. But I have downtube levers so this is not much of an issue for me.