We got an e-mail Friday from an Israeli site called Drippler with what looked like bad news for Apple’s (AAPL) new iPad:

Only 26% of Drippler users who own the 1st generation iPad plan on upgrading, while just 28% of iPad 2 owners will be getting the new iPad.

Given that Apple had sold 55 million iPads 1 and 2 as of last December, Drippler’s finding would suggest roughly 15 million upgrades — not a huge number considering the company sold 15.5 million iPads last quarter alone.

But judging from the rate at which the new iPad is disappearing from the 25 Apple online stores — U.S. and foreign — where it is available for pre-sale, demand seems to be at least as intense as it was for the iPad 2.

By Thursday morning, less than a day after it appeared on the U.S. store, ship dates for the 16 GB models had slipped from one day to three. By Friday, according to several sources, ship dates for all models in all 25 countries had slipped to anywhere from 3 days to 3 weeks.

Unless Apple has built way fewer new iPads than expected, a lot of people seem to be eager to get their hands on one ASAP.

So how to explain the lukewarm response on Drippler?

Well, it turns out there are a couple of problems with Drippler’s survey. First of all, it’s not a survey at all. Rather, it represents the number of iPad owners on Drippler’s site who happened to log in, notice that there was a new iPad listed, and click “Want it.” Drippler has more than a million members — most of them in the U.S. — but the company declined to say how many bothered to complete the three-step process that would have registered as an intent to upgrade.

We’ll get a better sense of the level of demand when lines start to form outside the Apple Stores next week. And if sales are particularly strong, we may get a press release from Apple PR the following Monday.

Last year, you may recall, there was no post-launch press release, and first-quarter sales of the iPad 2 — constrained by production problems — came in at 4.69 million, considerably less than expected.