According to this:

Unmanned aerial drones similar to ones used in the war on Iraq could be patrolling the U.S. border by the end of the year to help stem illegal immigration and increase security, Homeland Security Secretary Tom Ridge said Thursday.

Glenn Spencer's American Border Patrol recently ran a test using their own drone:

This month, Spencer launched a small, unmanned spy plane that includes cameras and a global positioning system to help him and other members of a private group called American Border Patrol identify illegal immigrants who try to slip into the USA across Arizona's vast desert.

Spencer says the $20,000 drone, which has a wingspan of 6 feet and still is being tested, will take off when one of dozens of ground sensors placed along the border detect foot traffic. The drone then will take photographs that will be relayed to U.S. authorities...

"Maybe I am a vigilante. I don't know," [a local rancher] says. "I'm not a racist. I'm an American citizen. If people could see from my perspective how the border is so unprotected. ... Everyone who loves this country ought to be doing something about it."

Although civil rights groups and some officials in the region have expressed concern about the government's acceptance of citizen patrols, Mario Villarreal, spokesman for the U.S. Bureau of Customs and Border Protection, says U.S. officials have openly sought help from local ranchers. He says the ranches have been urged to report suspicious activity, and to give U.S. agents access to their properties...

Mexico has "no official position," on the drone, says Miguel Escobar, Mexico's consul in Douglas, Ariz. But "I don't think anybody is very happy about it..."

U.S. Rep. Raul Grijalva, D-Ariz., has asked Attorney General John Ashcroft to investigate the private patrol groups, and says U.S. officials should do more to disassociate the government from such groups. "Every time the government accepts something from these groups" Grijalva says, "we further embolden them and give them credibility."

Expect the shrill, alarmist calls of racism and the like now endured by the private drone to be repeated with even greater force against the public drone. Pro-illegal-immigration groups - all of whom will be described as "human rights" or "immigrant rights" groups in media reports - will launch a broadside against the drone. They'll be joined by the Mexican government and corrupt U.S. politicians. As for Grijalva, he's a former member of Mecha; perhaps he's the one who should be investigated.

Hopefully Ridge et al will be able to withstand their assault and make this work.

As to why no one in the Mexican government would be happy with the drones, perhaps it's because its use runs counter to their strategy.