I don't find the screen size itself to be a problem. I moreso have an issue to with very high native resolution of the 27". I have terrible eyes and I find some menus and text to be quite small. I am holding onto hope that Apple will integrate resolution independence as a future feature of OS X.
The 27" screen is wonderful for watching movies, and I imagine that if you were doing video/photo editing, it would be quite useful to be able to see as much of the screen as possible, but as far as daily tasks that involve heavy text, I find that I strain my eyes quite a bit. As a temporary solution, I am currently using a default zoom extension in Firefox to compensate for the tiny text in my web browsing, at least. It's not ideal, but it works. I'm a recent Windows switcher and I am holding onto some of my old habits, for example, I still like my applications (including my web browser) to be maximized so that I can put my sole focus on the task at hand. Whenever I am doing anything with windows at their normal size, though, the higher resolution and extra screen real estate are great. In summary, I'll put it this way: If you have good eyes and smaller text doesn't bother you, the bigger work space and higher resolution are going to be a huge perk for you. If you're like me and like windows maximized to concentrate and don't have the greatest eyes, might want to see if you can try it out in the store. If the clarity of everything didn't turn to crap the very second that you run a monitor in anything but its native resolution, I would pop my 27" screen down to 1920x1080 and call it a day. For now, I am holding onto hope for resolution independence.
