I skiied Vail my first year on skis. I had some entry-level skis that I actually outgrew before I even hit the snow in Colorado. These two objects alone were bad bedfellows, but add in the fact that I didn't know my own abilities and you have yourself a dangerous combination.
Before you go on, just know that I didn't get hurt. Vail makes it obviously apparent when you are about to get yourself into a world of hurt. That aside, I still didn't hesitate to take advantage of some relatively fresh powder (Vail claims that it gets a lot, but in the week we were there we only got a good dumping once,) and try our luck on a treed-up black diamond. Not only was it the most fun I had ever had on skis before that point, it was also a turning point for my skiing.
Vail is a great big, expansive place. You can take a lift (or gondola) up one side and ski down the other, have lunch, and then ski to another area and explore. The area is literally a "ski town" and boasts some serious off-hill activies. Be sure to have a Fat Tire beer while visiting (I bought a keg).
Vail is the Microsoft of the ski industry, and that has its ups and downs--on the plus side, they take excellent care of their slopes, patrol their backcountry well (from what other friends on the trip have said), and are very friendly. The downside includes expensive lift tickets and food (in the villages), and big crowds. The colder months are a little less crowded but are also colder, so aim for late December and early January if you want to beat the crowds.