I think that having skied for many years and enjoy the high-speed schusses on steep slopes has helped my handling skills and to find the right line when cycling down big ascents.
Obviously whilst skiing, you´re almost never going to encounter something coming up the other way, so I think you need to have a better concentration on a bike than a pair of skis.
Cross-country skiing, as someone pointed out, is probably the most complete, all-round cross-training you can do, and will probably benefit anyone, regardless of their chosen sport(s).