To be anecdotal Mark Cavendish has been known to be distinctly suspicious of stretching because he believes that the tightness of his muscles assists in his ability to sprint. Not at all based on science or anything besides the 'what I am doing is working, so why change it?' mentality. But who are we to argue that? The results speak for themselves!
The debate is on going in terms of the benefits of stretching and performance.
I believe that it has been rather settled that cold stretching, prior to exercise, is at most detrimental to performance and at least pointless. A proper warm up where you cycle (literally I guess) through your various 'systems' is a generally accepted practice. See: protour cyclists before a time trial warming up on trainers, cyclocross racers prior to the race warming up on trainers (especially when we get to december/january/february racing) and so on and so forth.
A warmup that I find useful: pedal easy for 5 mins w/ power at 60% or lower of LT, 3 x 1 min fast pedals (focusing on technique, low power and high cadence) w/ 1 min recovery btw each, ride at an easy endurance pace for 5 minutes and then finish w/ a 5 minute 'blowout' (5 mins starting below LT, meeting LT at 1 min. point and then riding at VO2 max for last 30 seconds). Then you can get into the hard work. I typically do that type of warm up prior to threshold intervals etc...
In terms of stretching after exercise, it has worked for me. A quick scan through training manuals and literature seems to agree that post exercise stretching is of benefit BUT there is also a body of literature that points out that it has never been scientifically PROVEN that stretching post exercise is of benefit. For example:
My suggestion is that you do what works for you and that you are guided in your stretching by someone who is qualified to give you a stretching and strengthening program. I have often participated in pilates and yoga and find great benefits from a mixture of core strengthening exercises combined w/ lower body stretching. Grab a few books that can be trusted and do as much research as possible. Enroll in some studio based pilates/yoga courses that are run by certified instructors and see how you feel.
At worst you will begin to know your body better and get a feel for when you are straining or pushing beyond what your body can handle. In my experience a cyclist with a good amount of 'body awareness' is less prone to injury than those who just hop on the bike and hammer away.
Hope that helped a bit ...
To deal with the question posed below I thought I would add on. I ran out of space in the comments section.
I think it is because most of us are everyday working joes. Sure we ride way too much and some of us compete. But typically we have to either be on our feet or sitting at the desk, day in day out.
Cycling is incredibly repetitive and puts you in a position much different than that of your everyday 'healthy' posture. It creates muscular imbalances that can affect your pelvic tilt, your mid back, your neck and more. This can affect how you stand, how you sit and how you feel day to day. So for myself, I stretch so that I can feel better walking around, so that I can feel more like a functional human being. I stretch (and more accurately engage in pilates and yoga) as a form of 'cycling rehab' to try and correct those imbalances. As well that is why I cross train much of the year. From all of that I take it to, the better I feel day to day, the better I perform. And in my experience it has paid off in spades.
That said, if your spend 6-8 hours a day on the bike and the rest of the day off of your feet resting, perhaps you would prefer your body to become more oriented towards the position you take on the bike. But for the rest of us ...