I weight train with my cycling, but I do triathlon too so its also helpful for this. When I first started cycling I was coming out of bodybuilding, weighing 12.5 stone when my bodies natural weight is 10.5. My back and my neck were in agony for the first few weeks, used to picking up huge weight but not used to holding out for long. I changed my weights plan to include loads of body weight exercises,plyometrics and light weights. I go heavy sometimes (once every 9 days or so, but this is mainly squats, deadlifts and clean and press) just to hold a small bit of extra mass in my arms and shoulders but this is just a bit of vanity (plus it helps my swimming), I weight 11 stone right now and when I plan on racing I will be dropping the extra half a stone. Since changing my weights plan from heavy to more endurance based training I havnt had a single back ache, neck cringe and my arms can take the stress of wrestling with the bike up mountains. I would advise cyclists to train upper body with weights, it doesnt mean muscle gain, but it does help muscle strength and endurance if you train correctly and don't do any isolation moves which are designed to increase muscle mass. I train weights 1-2 times a week and its usually a full body workout, I think if I dropped the weights plan my cycling would suffer.... Even lance trained with weights for strength and conditioning.