The Adult Internet Market Research Company (AIMRCo) identified an " uncharacteristic" increase in spending on online pornography since the cheques were sent out.
Kirk Mishkin, head research consultant at AIMRCo, said: "Typically the summer is a slow period for this market.
"But many of the sites we surveyed have reported 20 to 30 per cent growth in membership rates since mid-May when the cheques were sent out."
The rebates were supposed to stimulate to the flagging US consumer sector, but it seems that many people are using them for a different kind of stimulation.
Jillian Fox, a spokeswoman for LSGmodels.com, one of the sites reporting figures to AIMRCo, said: "In a June 2008 survey of our members, 32 per cent referenced the recent stimulus package as part of their decision to either become a new member, or renew an existing membership.
"Getting more people to buy porn was probably the last thing Bush had on his mind when he came up with his 'stimulus package'. But we'll take it."