Ditto what the first poster said. I have the Kindle, friends have the Sony Reader, and both work fine here in Doha. You just download to your computer and transfer over to the reader.
Since you can basically use an iPhone like an electronic reader (I have another friend who does that here), I suspect there should be no problem using them with either PC or Mac formats. But check online to be sure.

Just my two cents: they are SO much better than books!!! Cheaper to buy individual texts, much easier to travel with... I got tired of waiting for a decent bookstore to come to this country. It never will. So cut out the middle man and just do it this way. Only wish I had gotten mine sooner!