WARNING: I'm in a USAir hub city & we have this card. They are changing ALL SORTS of their benefits, according to a mailing I got this month...basically half of what's listed on your link will be gone by Q2 2015 (companion tickets, first class check in, mileage booking discount, and (i think) Zone 2 boarding). Since those were the specific perks that were worth it for us, we'll probably be switching to another rewards card. Really disappointing changes on the horizon.
Anyway, back to the basic q. Airline miles can be converted to tickets which are "priced" by popularity of destination, timing of purchase, and timing of trip. Plus a whole bunch of airline bullshit rules and algorithms. Sometimes you luck out and only pay 45k miles for an international flight and sometimes it's 110k to fly 2 states over.
From my hub city to Paris-De Gaulle for that week a single ticket is 175,000 miles. I'd estimate a ~100 per ticket in fees/taxes, which you still have to pay. I, personally, don't think that's worth it.
I have the venture card from capitalone which allows you to use "points" to offset purchase price (of plane ticket, hotel, car rental, etc). It's not a great deal, because $1 = 2 Points at purchase, but you pay like 100 points for a $1 of redeemed value. I just prefer the flexibility of using that card vs being locked into 1 particular airline. We use credit cards for everything possible, so we rack up points pretty quickly.