Apple’s per-hour total for iPad pre-orders could be somewhere in the range of 15,000 to 25,000, according to bloggers who have been tracking order numbers. The initial efforts began at Investor Village’s AAPL Sanity Board and Silicon Alley Insider; the former came in at 25,000 per hour and the latter at 20,000. (AAPL Sanity Board requires a membership to view its postings.)

AAPL Sanity member Victor Castroll, an analyst with Valcent Financial Group, set up and monitored a Google spreadsheet with help of other board members. Using their own order confirmation numbers, they figured 51,000 orders in two hours, after taking an educated guess at the non-iPad orders that would have to be tossed, according to Fortune’s Philip Elmer-DeWitt.

Meanwhile, Silicon Alley Insider spoke with Andrew Erlichson, CEO of the photo sharing web site Phanfare, who said: “We just bought two iPads, about 30 minutes apart. Our order IDs are 10,000 apart. Assuming those order IDs are sequential, and they appear to be, then Apple is selling 20,000 iPads per hour. Assuming most orders are for the US$499 model, and that people are only buying 1 per order, that means Apple is selling $10MM/hour. Of course that is not sustainable, but if they did it for a year, it would be $87.6B.

“Now, of course, we can’t be sure every order was for an iPad. Apple does sell other stuff. But at 830am in the morning on the east coast, my guess is that most of the orders were for iPads.”

The order tracking continued over the next few hours, and Silicon Alley Insider posted another piece with a pair of estimates via Mr. Castroll: 74,000 iPads in the first four-and-a-half hours, or 16,000 per hour, and 91,000 iPads in six hours, or 15,000 per hour. This would suggest the initial flurry was beginning to die down, which isn’t surprising.

Mr. Elmer-DeWitt noted that supply chain rumors suggested Apple may have only 300,000 units for sale at the iPad’s launch on April 3, so those pre-order estimates could mean it will sell out before then. Quipped Silicon Alley Insider’s Jay Yarrow: “You can be sure it will put out a press release on Monday if it sells 16,444 iPads per hour all weekend.”