I forget exactly how it goes but two in a prius is better for the environment (I think) than two in a full jet but it's pretty close I think. As far as time, chicago to the continental divide is a little over 1000 miles. If you fly to Denver, get thru rental car hell, and everything goes perfectly (no delays, bags make it, rental car hell goes OK, etc.), sometimes you can hit the slopes at Loveland by noon. Once in awhile 11:30. But you have to get up at 2:30AM to make it an things have to go just right. My dad and his buddy are into driving it, leaving at 4AM, getting to Denver by 6-7PM, getting a good night sleep, then hitting the snow on day 2. So it can be worth a solid half day if things go just right. You're wrecked by the night on day 1 but you've gotten some riding out of it. Coming home...well you can usually go until 1 or 2, buzz down to Denver, make it to Ohare by 11PM, then home by 1AM so you can get another 3/4ths day in at the end vs. driving. My dad and his buddy will ski until 3PM, drive until 10PM, then finish up getting home the next day. They drive the speed limit in his caddie and get about 25mpg for the whole trip and don't ever feel totally strung out from air travel and getting up at 2:30am, getting home at 1am.
So if it's a 5 day trip, I guess us in Chicago are stuck flying but if it's a week, driving starts to look really good.