I have a Macbook Air, iPhone and 3G iPad (though I've only used it WiFi at this point). I also bought the bluetooth keyboard.
I also have a Kindle DX (the large one) which I use for reading.
I have used LogMeIn Ignition and iSSH on my iPhone to connect to clients machines when "out and about" -- times when I've not had my Air but would probably had my Kindle so now I will (hopefully) have my iPad and will be much more efficient.
I tried loading some reference documents (mostly PDFs) on the Kindle (which is why I bought the DX) but the Kindle doesn't really (yet) handle PDFs well. The iPad does. I can easily zoom, scroll, search, etc. my manuals.
I have a couple of bicycling trips to Germany this year -- one is a week long tour where I will take the iPad and keyboard and save weight. That is the main reason I bought the 3G version (hoping somebody in Germany has a micro-SIM and a decent data plan
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When flying, I've watched movies/TV shows on the iPhone but it will be much nicer on the iPad. I view it as my portable In Flight Entertainment system (I just read were a company plans to rent specially loaded iPads at airports for entertainment). I can watch some shows, read a book, play some games. All of which I could do on the iPhone but better on the iPad.
During the NBA playoffs, She Who Must Be Obeyed has first crack at the HDTV. If I want to watch something from my HTPC (a Mac Mini) I could do it at my computer but with the iPad I sit in a comfy chair in the living room and stream using Air Video.
Is it perfect? No. It needs to be a bit lighter and a bit cheaper, but that will come. There are things that piss me off (why do I have to email Pages/Numbers documents to myself rather than just transfering) but all in all I've had the thing just over two weeks and I can't see being without it.