I know that this subject comes up many times on the board, but just wanted to share this link from American Orthopaedic Society for Sports Medicine (AOSSM).
In the article, post-surgical and functional bracing is discussed as well as sleeves. In general, there is little empirical data to support bracing; however, skiing is discussed as one area where a brace may be beneficial. The article is less than 4 pages and I felt that it was a very good read.
The following articles are referenced in the above article:
Effects of functional bracing on knee injury in skiers with anterior cruciate ligament reconstruction: a prospective cohort study
Effect of functional bracing on subsequent knee injury in ACL-deficient professional skiers