So I was one of the posters in the original spirited discussion. And I'm going to comment on a few of the things I said there, here:
1) resistance training is very important for bone mass
2) also important for increasing the tensile strength of tendons and ligaments to prevent injury with forceful movements (someone else mentioned this here as well)
3) is an effective way to increase the number of muscle fibres available for recruitment during cycling, that is, there is a beneficial neuromuscular effect to increase endurance that cannot easily be obtained another way unless you're willing to ride 6 hours a day like Lance did
New things that I would add specific to this discussion:
4) plyometric and ballistic movements when lifting weights are beneficial for increased effective use of fast twitch fibres that give you that short burst of speed when you need it (eg sprint end to a race)
5) I would reiterate the importance of core training for two reasons. You're likely to hurt yourself with ballistic motion or plyo if you don't have a strong core and a strong core translates into better application of power to the pedal (it's like having a stiff sole on your cycling shoe vs a squishy sole)
So in the end, yes I believe lifting weights is a good thing but I don't agree with ballistic lifting unless you are trying to increase sprinting power. Slightly faster lifts may be more beneficial in that you are recruiting the muscles at a speed closer to what you would use in cycling.
There are a bunch of people out there doing crossfit workouts, these are great, they combine better core work and faster movements (but not necessarily ballistic). I think these are very good workouts but you definitely need to be careful to modify the weights used to allow you to do the movements safely. I know a crossfit coach that recommends at least 3 months of doing the workouts with a bar only for things like squats and deadlifts while focusing completely on form, before you ever think of doing anything adding more weight than this.
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