As a college student in Colorado, I have flown into Aspen many times on United Express (BAE-146's out of SFO, sometimes CRJ's). Although I have never personally flown an airplane into either of those airports, I have talked with many glider and airplane pilots about mountain flying, specifically Leadville and Aspen.

Aspen represents all the challenges with mountain flying. Within a close vicinity of Aspen lies terrain the stretches from 12-14,000ft. It is very important to know WHERE you are where the TERRAIN is when flying into Aspen. Aspen's runway 15/33 is slightly over a mile long (7,000ft), and yet there is a 200ft vertical rise. At an altitude of 8,000ft, it is not uncommon in the summer to see density altitudes in excess of 12,000ft! Better approach with your engines turning. Now throw low visibility into this crazy layout, and you have Aspen.

A much steeper than normal glideslope is required, not only for the reasons above (terrain, etc...), but also because of mountain winds. As a glider pilot, I know that a change from the upwind to the downwind portion of a mountain wave is a difference between a 1000ft/min rate of climb to a 1000ft/min rate of descent. Add in strong downdrafts like these, and you want to have a big margin between you and the mountain terrain. There are also noise abaitment considerations.

Hope this helps,
I plan to take a mountain flying course this summer so that I can fly in and out of airports like that.
Ryan