Having just come back from holiday in Brittany where there were no flats at all, I suddenly find myself enjoying hills as well, like quite a few of you have mentioned. And I'm sure the reason is quite as much psychological as physical.
However, one thing that was really daunting was entering the local 10K which took place on the third day there - and we're talking a really small fishing village here not some big metropolis and there's me thinking I've got a good chance of placing quite well - and finding myself utterly outclassed on the hilly two lap course. These local guys were literally swarming up those hills on a seriously hot day, without slackening the pace (like I was) - it really brought home to me that to race hills you've got to train on hills, which I guess is kinda obvious, but somehow one hopes is not really true.
Hilly's point about becoming a slower hill runner from running too many hills day in day out is an interesting one - but I think the answer to that is to make sure you also run hill repeats, the more gruelling the pace and the incline the better. I always find this makes the biggest difference to my running not just up hill but also on the flat, whenever I can face the agony of actually doing them. I do think that if you're always running hilly circuits at a training pace then you could well end up a slower runner - running too slow too often actually teaches the body to run slow and suppresses its ability to run faster, whether you're talking about hills or not.
enough of this - it's too exhausting even to write about. thanks goodness my next race is nice and flat (I hope). s.