Or any other reader, really, like the Sony's or the Nook. The Kobo is sold at about the same price as a Nook but is limited in a number of very annoying ways (no book wide search, no way to jump to a particular page etc.)
That's fair. Those are some major features. I don't find them to be of any particular hindrance though. Frankly, I find I read more quickly on the Kobo, as opposed to traditional book formats.
I can connect my Kindle to any Mac, Windows or Linux computer using a USB cable, the OS sees the Kindle as an external drive ... You can transfer as many documents as you want to your Kindle this way (actually as many as your Kindle can store, about 3GB for a Kindle 3).
You can read PDFs on the Kindle fine.
You can read them, but unless you have the dx it will be difficult. I much prefer the experience of goodreader on iPad.