Some 6,635 consumers have reserved the all-electric Nissan Leaf since the reservation process began on Tuesday, Nissan North America Inc. says.

Right now, the reservation process for the Leaf, for which prospective buyers are asked to put down a refundable $99, only is open to those 115,000 people who pre-registered their interest in the EV.

Nissan will open up the registration process to everyone on May 15.

The auto maker hopes to have 20,000 Leafs spoken for by the time the car goes on sale in the U.S. in December, NNA spokesman Brian Brockman says, adding Nissan is “well on our way.”

The process to reserve a Leaf apparently has not been without hiccups.

People wanting to reserve a Leaf took to blogs this week, reporting frustration with the process.

Complaints include the inability to input American Express credit card numbers on the Leaf’s reservation website, inoperable links and long wait times on the phone.

“My question is, with all of risk associated with being an early adopter of new technology, why would Nissan choose to present themselves this ineptly?” an irritated poster on a New York Times blog writes.

Brockman says the American Express issue has been resolved.

“If customers still have a problem accessing the system, we’re asking them to contact customer assistance, who will help them either get into the system or take the reservation over the phone.”

Reports indicate reservations largely have come from “smile” states, those along the West and East Coasts and in the southern U.S.

The first Leafs in the U.S. will be imported from Japan and directed to certain regions, including the states of Oregon, California and Tennessee, as well as Seattle, Phoenix and Tucson markets, Mark Perry, director-product planning for NNA, tells the Times.

Prospective buyers in Georgia, Texas, North Carolina and Massachusetts then will get their shot.

National rollout of the Leaf is set for 2011, with U.S. production at Nissan’s Smryna, TN, plant to begin in 2012.