Before the permanent late shift was introduced three years ago (which I volunteered for as soon as the form became available), I always tended to plan my vacation for early shift weeks. Since the majority of the people in most departments prefer to work early shift and thus tended to plan their vacation for late shift weeks, there were usually enough slots available for me to get my request fulfilled.
I was promoted last December, so this past year is my first with the company where I've been able to get whatever vacation I wanted. Instead of competing with 100 other people, there's now only 1 (out of 3 others who share my job) that's been in the building longer than me, and so has first dibs at weeks. It's pretty easy to work it out between ourselves before we give in our requests, though
So a few of the same rules, a few different ones. For regular employees, requests need to be in by January 15th. If they are, those are doled out based on seniority. You're only guaranteed 2 weeks in "prime time" (basically June, July, August). Anything submitted after January 15th is given out first come, first served based on availability