I have shoulder length hair. What is the appropriate way to wear it in formal situations such as weddings, interviews, or dinner parties? Do I need to wear it in a ponytail or can I wear it loose? For some reason, I am more comfortable with it loose, but I want to still look formal, and I don't want to break any fashion etiqutte rules.
A pony tail would be ideal but if you tuck all your hair over your ears (you may do already) and have it fall over your back I think that'd be acceptable.
A great longhair style for formal occasions is to French braid the front and sides, leaving a curtain of loose hair in the back. Here are a couple sample ideas (they will work for shorter hair as well as for hair as long as pictured):

The braid idea is not a good one, if it looks like the picture. You don't want to appear comical. The ponytail with pulled back over ears is the best. If you have any frizz, then finger some mousse through it and it will look great.
Here's my recommendation. Wear a ponytail, but use one of the larger style ponytail holders. MUCH more comfortable than the thin ones. You may think it's "feminine" at first, but as long as you get something that isn't in a pastel color, it'll look pretty nice (as well as somewhat formal) and still look masculine. Also prevents headaches, which I get if I wear the normal thin ponytail holders.
-J (currently ponytail-less, but returning to how I should always be)