My $0.02: hills (and riding in general) are at least 80% mental. I agree with all the other stuff here...but remember that your head can be your most valuable ally.

In the last place I lived, we had nothing but hills. The only flat stretch was Main Street downtown, which was about 0.75 mile long. And the pavement was awful (small, rural jursidiction). I only rode that part when I rode to work.

Riding up hills is hard work. Why would anyone in their right mind choose to ride up a hill? I had no choice (well I did: not to ride at all), so my mindset was "I'm going to go for a ride" not "I'm going to go ride a route that has hills! Eeeek!". I became a very strong hill climber because that's what I rode all the time. I have a triple and am not ashamed. I'm a believer in weight training and pushups to help build strength and muscle endurance.

Now....having said that...I must say that I have issues with the flats. And I know that most of these issues are in my head. You get no breaks on the flats (like you do when you are going downhill, the reward for the uphill)! They lack in variation (I was used to shifting often...you don't do that on the flats)! Headwinds and crosswinds! Riding the flats hurts my butt! But I know that in order to go faster on the flats, I have to wrap my head around all of those things that I dread about them. Someday I'll be faster. I just have to train my head.

Where I live now we have a mixture of flats, rollers, and what I call hard (but not extreme) climbs. Frankly, I miss my old riding territory. When given a choice here, I have so far selected routes with more hills. In this new place, though, I'm going to have to find something else to focus on since my 2500-feet-on-every-ride situation no longer exists.

So don't give the hills your mental energy...put that energy to better use. Just think of it as a ride!