“I wouldn’t bet against this product,” said Piper Jaffray Gene Munster in the press scrum after Steve Jobs’ presentation Wednesday. But when asked to estimate how many units Apple (AAPL) will sell this year, Munster — one of the Street’s more bullish analysts — put his marker on 3.5 million.

Three and half million devices at anywhere between $499 and $829 apiece is nothing to sneeze at, of course. But by comparison, Apple sold 3.36 million Macs, 8.7 million iPhones and 20.1 million iPods in the last quarter alone.

Jobs set a high bar for himself on Wednesday: to create nothing less than a new computing category in the space between a laptop and a smartphone.

The iPad is that. Without a keyboard, a DVD drive or any of the usual ports (USB, Ethernet, etc.), it’s less than a laptop. Without a camera or a cellphone plan, it’s not a smartphone. And it doesn’t fit into any pocket we own.

Don’t get us wrong. The iPad is a lovely product. The screen is gorgeous. The build is tight. The apps are fast and there are already loads of them — virtually all of the 140,000 written for the iPhone and the iPod touch, according to Apple, will run on the iPad. The promised 10-hour battery life sounds too good to be true.

(It may be; Steve Jobs said he could watch videos on his iPad all the way from San Francisco to Tokyo and still have juice to spare, but as the New York Times’ David Pogue points out, that flight takes 11 hours.)

The question you have to ask yourself, however, is this: if you already have an iPhone and a MacBook, why would you need an iPad? Or, to put it another way, if you are thinking about buying your daughter a computer, would you buy her a netbook, a MacBook, a Windows 7 computer or an iPad?

You answer may vary. For me, the lack of a physical keyboard is a deal breaker. The virtual keyboard is a little better than the iPhone’s, but not much.

Apple sells a $69 external keyboard that works quite well, but when you start adding accessories, the device starts to lose some of its essential elegance and the price point changes. Do the math: with a 64 GB iPad with 3G connectivity ($829) plus keyboard ($69) you’re up to nearly $900, more than the student discount price of a new MacBook, even before AT&T’s $30/mos. data plan.

Munster, for one, thinks that the iPad actually competes not with the MacBook, but the iPod touch. In a report issued Wednesday afternoon he’s estimates that for every 2.7 million iPads Apple sells in 2010, it will sell 1.8 million fewer iPod touches.

We may not find out if he’s right until next September, which is when Apple reports the first full quarter of iPad sales.

For hardware specs and pricing details on the new device, see Apple’s press release here. For our coverage of Wednesday’s event, see Live: Steve Jobs presents the Apple tablet.

[Follow Philip Elmer-DeWitt on Twitter @philiped]