<font face="Verdana, Arial, Helvetica, sans-serif" size="2">Originally posted by Eugene:
Excellent memory, Gary! 
That was actually not an HBR article, but a very interesting Harvard case study called "Hilton HHonors Worldwide: Loyalty Wars", and discussed not just HH, but also SPG, and other key players in hotel loyalty programs game. It was available online, but it looks like it's gone now. Wish I have saved that pdf file...</font>
It's actually available online at Harvard Business Online. Just google the title of the article. You may have to pay a nominal fee to D/L the article.