To the OP - I would seriously caution against staying in Dillon/Frisco/Silverthorne. As I recall, each is about a 20 minute drive from the skiing. You then have to park up and may need to take a bus to the slopes (I know the gondola has gone in at Breck since my last visit, so this may make things a little better, but it's still going to be a pain). Taking a break mid-afternoon back at the room will be a non-starter and with the dollar still so weak you should - IMO - just make the most of it!

As for comments re: Altitude, I've been across with different groups of people on several occasions and the majority have been OK, but it seems to hit people in strange ways. I'm not going to start a debate on the matter, just stating that one of my mates could barely put his socks on without breaing into a sweat and whilst he's no athlete, he's not Homer Simpson either...