I never USED to stretch. When I ran in high school or by myself I'd just finish up the run, sit down for a few minutes, then continue with my day.

In college we'd briefly stretch before a hard workout (after a warm up) and then after the hard workout. You would always stretch before a race. I'm going to tell you this now. MOST if not ALL professional and collegiate runners stretch before their race.

Now-a-day I stretch after running but not after cycling unless I was REALLY hammering it. (Like, can barely get off the bike hammering it.) If I don't stretch after running I will tighten up in the next hour and then I'm tight the next day, and I don't like that. (Anecdotal evidence of course.) Cycling seems to be a lot more forgiving with not stretching. I also bike to work everyday, so I loosen those muscles at least 3 times a day.