There have been some people pointing to how this could parallel the iPhone, which they say didn't take off like a rocket. Apple did sell 5.4 million iPhones the device's first year, and I'm not sure that counts as sluggish. But even with some analysts guessing that the iPad might sell in the neighborhood of a few million in its first year, I think that there is even more potential, only the current positioning as "another" category of device is too vague. In this sense, the iPad is like the Mac when it first came out. Getting oohs and ahs may be nice, but ultimately you have to convince people that they need the product. Even if the need is mostly emotional, people must have at least a logical rationalization to justify the desire. And that comes from third party software defining clear niche uses for the iPad.
Notice I'm not saying that there was no real need for the Mac. There was a reason that many artists, graphic designers, writers, musicians, videographers, production staff, and others gravitated to the machine: software. Although now most if not all of the specialized applications you need for "creative" activities are available on PCs, that wasn't always the case. Because there were things that these people could do on a Mac that wasn't possible on a PC, they joined Apple's camp.
Success for the iPad requires exactly that to happen, only it can't be the result of amorphous assertions that you "have to hold it in your hands" to understand. The possibilities seem to be there. I draw and paint in my spare time and suddenly had a flash of what it might mean to have the bigger screen running Brushes, the iPhone painting app. (I also had a flash of iPad want.) Given the size and weight, it could become a great alternative to a sketchbook and pens or watercolors if you ultimately wanted digital results, and you wouldn't need to be tied to a computer because you could load the results over later. It might be that a stylus would actually be helpful (it might give a more precise point of input), but with a touch screen, that would seem relatively easy to implement.
Some other uses quickly come to mind. Photo or video editing. Writing (with a more easily portable keyboard). Location sound recording. Or it could be working on a business plan spreadsheet away from the desk using cloud software over a Wi-Fi or 3G connection. The point is that these uses start defining actual market niches in which a laptop may not have enough input flexibility but a smartphone is too small.
I suspect the reason a ramp-up of the iPad could take a while is because it will largely be the third party software vendors who will have to create these definite images into which potential customers could project themselves. Unlike the iPhone, where having a choice of single apps was a driving factor in its market growth, the iPad needs something like "there's an app suite for that." Then the iPad isn't a new category of device for everyone, but a specific category of solution to the needs of particular groups.
Image via stock.xchng user nicootje, site standard license.