What a good topic. I've found the same thing, especially since I face inclines soon no matter how I turn from the driveway. For me, it's about 20 minutes of thinking "whose big idea was this, I'm lousy, blah, blah, blah" and then...then...

The trainer I work with, the masters champ, is FANATICAL about long warm ups. I think that even if you're younger and can get away without them, your body will hold up better in the long run if you warm up well.