There's already a reasonable selection of magazines (especially SF and mystery magazines) available in multiple formats, DRM-free, from http://www.fictionwise.com . These can be read on any of the popular bookreaders - Sony, Gen3, or Kindle.
Fictionwise does a great job with what they have available. My hope is that the 'Kindle-effect' will spread newspapers and news-type magazines to Fictionwise after the publishers see some success with Kindle editions. There are several regional (US) newspapers I would like to subscribe too electronically.
Back to the Mac compatibility thing: it seems like Amazon and Bookeen (Cybook) went out of their way to make their readers cross platform compatible. Sony seems to have lost the hunt on that score but they seem more interested in locking users in to their device and store. iRex surprises me because at the price they are asking you would think they would insure cross platform compatibility.
There is a rumor that Apple will come out with a tablet computer and I had been holding off because of that, but that rumor has been knocking around for a couple of years now and I'm just not going to wait for vaporware. Hence my decision to try the Cybook with my Mac.
As a side note - because the Cybook does not need special software on my computer for ebook conversion it means that I can use any of my 3 computers to add ebooks to it as I find them. I'm not just tied to a computer that has their software pre-installed. I like that flexibility.