United Mileage Plus members can earn 1,000 bonus miles when spending between $500 and $749 at 20 participating retailers at http://www.mileageplusmall.com through Dec. 21, 2009. Spend $750 to $999 to earn 1,500 bonus miles and 2,000 bonus miles when spending $1,000 or more. The maximum bonus you can earn is 2,000 miles.