Something I just noticed this weekend, as a matter of fact. I ran Saturday, then came home, showered and put on a bathing suit. I met my dd for a swim at the beach, and we both checked each other out. We both noticed that this one varicose vein I have behind my right knee is much less noticable. She even asked if I had rollerbladed - because the knee pads I wear could compress it. So, I am of the "running made mine better" camp.
I also have a good friend who showed me his leg on a Sunday, after a run. Said maybe a torn muscle? Swollen and warm to the touch. He was an avid runner. He went to bed and never woke up. His wife said cause of death was a blood clot in the calf. Do not ignore symptoms!