Maybe it's just me, but aside from aerobic benefits and the nice variety that comes from any kind of crosstraining, I don't think running and biking compliment each other much. I find that if for a week or two I don't ride my bike, but have run quite a bit, my spin is crap when I first get back on the track bike. The same situation seems to happen on the flip side, I'm running, but my legs are thinking about pedaling in little circles, so my stride seems a bit funky for the first few clicks.
I've read that different muscle groups are used for each activity, so I'd think the strenght gains from one would not necessarily help the other either.