I've been a runner for about the last 10 years. I run about 20-30 miles a week, year round. I am just starting up cycling again after a loooong break.
In regards to running, I am finding that it is actually improving. Even though I stretch a bit after a run, my legs feel much better since I started cycling and my long run times are dropping. Some may be due to it seems that cycling works the "core" part of the body better. (?)
As for cycling, I just started about a month ago and I ride 3-4 times a week. I am up to 30 miles at what I consider a brisk pace. I am suprised that I was up to this pace fairly easily. I'm sure the cardio from running is 90% of it.
I want to get increase my cycling more as the weather gets better so I will probably decrease my running to 2X a week. We'll see how it goes!
Ken