Negatives? A few. Mail seems slow to come in. My MobileMe mail will ping my desktop and my iPhone at the same time. Then a minute or so later it will show up on the iPad. Don't know why this is happening, but it is pretty consistent and it should be fixed. I also don't like the 15 minute wait before the iPad polls a POP account. I'd like it to offer 5 minute and 1 minute options just like Mail on OS X.
I'd like to see some of the buttons and menus have an option to be placed at the bottom of the page, rather than the top. The way I have the iPad on a table, it's a bit of a stretch to get mail sent or forwarded. It would be much easier from the bottom. It's no big thing, just something that would be nice.
Speaking of iPads on tables, I think a lot of people will really need a stand. I looked at the Apple case, which has a sort of stand built in, but I thought it looked cheap and not worthy of an Apple logo. I finally grabbed a study stand at a nearby Barnes & Noble, which is designed for books, but does OK with the iPad. The pad is just too heavy to hold one-handed for any length of time. By the way, I don't see the little $5.99 book stand in B&N's online catalog, or I'd give you a link, but I think the local stores have them.
The photo app doesn't really do much. I'd like something similar to iPhoto. There are some good 3rd party solutions I've looked at, but I think it should be a basic part of the iPad. I know there's no camera on the iPad (damn!) but I'd still like photo editing choices, especially with the ability to download camera images with the upcoming camera adapter.
I think the biggest drawback is the lack of multitasking. I know it's coming, but Fall 2010 is a long way from now. When you are in the middle of something and mail comes in it's just too much fooling around to back out of what you are doing and read or respond. I'm hoping there will be an option for a pop-up so I deal with messages as they come in. Some won't want the interruption, but it should be an option.
I think the iPad is a major win for Apple. It's a bit rough in spots, but this is version 1.0. It's more than just a big iPhone without the phone. It's a design that will get emulated over and over by the competition, who likely won't get it right, but will continue to put pressure on Apple to expand and enhance this newest member of the Apple family.