As far as reading PDFs on Windows goes: evince (default on Ubuntu, I think) works really well - it's fast, remembers my position in various PDFs, and in general works really well.
A million times this. In fact, even as a windows user, preview on OS X is the best PDF reader there is.
I'm note sure it's the format over the technology to start with as it's quite complicated to lay out technical material effectively so it requires some human intervention to a standard which doesn't make you want to poke your eyes out. PDF is just paper on a screen which takes the layout engine and automation out the back and shoots it.
Depends on the book. The Kindle isn't great at pictures, graphs, or complex diagrams, and examples with code might lose formatting via smaller dimensions.
However, it's still convenient to not have to lug around a giant text book to read somewhere - any of them. Having a Kindle is like having your entire library with you at all times.
I've been reading technical books on it for a year now. Currently reading through a few Haskell and Scala books for fun (all pdfs). I wouldn't recommend picture heavy textbook, for example something on Biology, but for Comp. Sci. books it does the trick imo.
I don't know if is the fault of the format(mobi) or they are really bad at formatting technical books.