I bought an iPad back in May and I've been _extremely_ happy with it. And I've used it for rpgs at the table.
I originally bought it because I wanted a kick-ass ebook reader "with benefits". One critical thing for me was pdf support for rpg pdfs. See, rpg pdfs are special because people insist that rpg books be part encyclopedia, part coffee table artbook, and part textbook. Plus there's the bookmarks, selectable text, and probably other stuff I'm forgetting.
I've been buying pdfs for years and don't own a laptop. Not keen on 'em either, because I've seen too many people more focused on the laptop than the game. I also don't really like the seperation that a laptop at the table brings; I'm not a fan of GM screens for that same "seperation" reason.
For rpg stuff, I've primarily relied on Good Reader as my pdf viewer. It's been a total champ and has gotten the ability to make notes in the pdf. It handles built in bookmarks and you can add bookmarks as well.
One thing to watch out for on pdfs is the layers thing. Some companies (0One for example) use layers in pdfs to turn off and on options; Mad Irishman uses it too for some of his character sheets. To my knowledge, form-fillable pdfs and layered pdfs don't work in any fashion. They're "frozen" with the bits already filled in (or blank, depending on whether or not you've already filled in a form-fillable pdf) and whatever the default layered pdf options are (or everything showing).
At the table, it's nice to be able to refernce rulebooks as needed and be able to carry a large chunks of books without it actually weighing anything or taking up space at the table. As a general rule, these days I refuse to buy physical product; if I can't get it digital, it's gotta be plenty exceptional for me to consider it. For better or worse, that mean I don't give WotC money these days.
I also sprang for the Battle Map program. Yeah, it's expensive, but it's pretty incredible what you can do with it as well. One advantage it has over the Map Tools project, is that the Map Tools project relies on having another computer. Battle Map has a GM and player mode that you can toggle between. If you're seriously into miniature-based gameplay (I'm not, even though I bought the app), it's pretty spiffy.
Don't think of it as strictly a mapping program though. You can import objects and backgrounds into it. Which means for example that if you're lazy, you can just import you battlemap as a background image, slap some tokens on top of it and call it a day.bif you're looking to be more creative, you can use it as a character sheet. Just import the sheet as a background, and then have some custom tokens to take care of the little bits (HP or whatever) that you actually change/adjust. Since you can give tokens colors to represent status or whatever, you can also have it act as a tracker for things as well. Use a power, turn off (or on) the color of a custom token set next to the power, or whatever.
If you're motivated, clever, and/or willing to spend a few bucks, you can get an amazing amount of use out this thing. Programs for recording audio (handy to save a game session for whatever reason), simply loading music/soundclips onto the iPad if you're into that sort of thing, reference photos, connecting to the net to show something (if you've got WiFi access, or are carzy enough to buy the 3g version).
Weight wise, I've found it plenty comfortable. The battery last 8-10 hours easy, color is good. Direct sunlight or ultra bright light can be a problem.
Is the iPad perfect? Nope. Nothing is. But for what I need and want, it's pretty killer. Getting beneifts like web browsing, email, and all that other stuff is icing on the cake. At this point, the iPad doesn't just handle my rpg duties, I don't even bother flipping on my computer unless I need to actually create something or if I feel like playing a PC game. For the low level computer stuff of browsing, forum posting, etc, I use the iPad. A decent RSS app (Reeder) hooks into my Google Reader, so it's extremely easy to keep up on the forums as well as news.
And I say all this as a dude that actively dislikes Apple; the iPad is the only Apple product I've ever bought for myself. The iPod that I've got is a 1st gen Nano that my wife gave me after _she_ bought a new one.
I love what my iPad does for me, both at the gametable and away from it.