Here's a copy & paste of their response when I inquired last month:
On Wed, Dec 9, 2009 at 3:57 PM, PokerStars Support <firstname.lastname@example.org
Thank you for your email.
Regarding your question about rakeback, PokerStars does not offer this type of promotion to our players.
Please understand there are many conditions to rakeback deals, and such promotions must be paid for somehow. Usually this means higher rake charges in large pots, higher tournament fees, and/or reduced value frequent player programs. Most sites that offer rakeback will also deduct rakeback paid to players from deposit bonus payments or charge far higher redemption prices for items in their VIP programs.
Instead of rakeback, PokerStars prefers to simply offer the most competitive "base" rake in the industry and an extensive VIP program with the highest value player rewards available. If you compare the rake charges and rakeback conditions across sites, you will find PokerStars' rake to be the best deal for players. To view PokerStars' rake charges, please visit our website:
If you are interested in cashback deals, perhaps you would be interested in the PokerStars VIP Store cash bonus offers? These cash bonuses are available to any player whose VIP status is SilverStar or above, and players can purchase them using their Frequent Player Points (FPPs) earned in real money
games at PokerStars. For example, a SilverStar VIP can purchase a $50 cash bonus for 5,000 FPP. In many cases, these cash bonuses are of greater value than any rakeback deals. For complete information and conditions, please visit the PokerStars VIP Store cash bonus web page:
If you have never heard of the PokerStars VIP Club, then step right this way:
While we hope you are convinced already, remember also PokerStars provides the widest variety of games with the biggest prizes available online. Additionally, we believe that nowhere else on the Internet will you find a site that has put more effort into ensuring its games are fair, nor which has a higher regard for integrity or commitment to customer service.
Should you have further questions or concerns, please don't hesitate to contact us again.
PokerStars Support Team