Originally Posted by JP513

I think the Mileage Plus card has a higher level of membership than the standard card. You pay a much higher annual fee (around $140 v $60) but in return for that, you get the Platinum class card and 2 miles per $ spent instead of just 1.

Read about it here:

http://www.united.com/page/article/0,10017,3865,00.html