United is selling miles with the following discounts

• save 20% if you buy up to 25,000 miles
• save 40% if you buy more than 25,000 miles

Offer ends June 30, 2013

Click here to sign up

But, is this a good deal? Buying miles is rarely ever a very good deal. Lets take a look

Example 1:
Buying 25,000 miles costs $564, or about 2.3 cents per mile. You can usually redeem 25,000 miles for a domestic flight. If it often difficult to get this much value when redeeming miles. Said another way, if you were to redeem 25,000 for a $564 flight I would say you are getting a good deal. If the flight was only $300 I would tell you to pay cash and save your miles.

So the decision is easy: If there is a domestic flight that you want and it costs more than $564, you might save some money. However, you will have to deal with the hassle of finding reward seats and you don't earn miles on reward flights. If your flight is $900 and there are reward seats available, I would buy these miles in a heartbeat.

Example 2:
Buying 100,000 miles costs $2,257. If you are looking for a business class trip to Europe which should cost 100,000 miles, you might pay much more than $2,257, maybe $3-4k even.

In summary, like usual, its probably not worth buying miles. If you need a few extra miles to redeem for a flight it might be worth it.