If you don't want to own a Mac because you can build something better for $50, you're not going to buy this anyway, so I'm not completely sure what the comments are all about, and perhaps you should save them up for the Dyson vacuums that show up four times a week, where you can post how much cheaper a broom is and how it sweeps better under couches.
If you're not going to buy a Mac because you prefer Windows, that's a fine preference to have, but it doesn't really impact the decision-making of those who might want to buy this unless there are things they want to do which they wouldn't be able to do with this system (which could very well be the case).
Stepping out of the flames for a second:
If all you do is surf the web and write email and are not especially a fan of any given OS, then this is an expensive purchase unless you want to place it somewhere more "public" in the house, in which case the quiet and the aesthetics (and single cord) might be important. Otherwise, find a good Windows 7 box and install a decent antivirus scanner on it. You'll be fine.
If you are used to Windows and know every in and out of using it, you might find OS X jarring. If you're a casual user, you won't. My parents, for example, seemed to always be perplexed by Windows (XP, I think, at the time), but have no problems using their Macs now (that said, it always amazes me to watch them use the OS, because they really don't take advantage of it and do things in ways I consider awkward, but... they are comfortable with it all, so that's what matters).
If you have to have the bestest tech, then you need to know this will be upgraded in a few months. From a CPU point of view, it's doubtful much will change of significance, but maybe they'll add USB3.
That said, this is a good discount on a good computer which will serve most people very well. It is well-built, silent, attractive, and the Thunderbolt interface opens up faster-than-USB3 speeds, chaining monitors and hard drives, and so on... but it's still pretty new, and things are just starting to come out that use it effectively. It's something you'll likely use in a year or two but probably will not use right away.
It'll play all but the most GPU-intensive games. It'll run Flash, it'll do most of what you want with the built-in apps. The App Store makes it brain-dead simple to buy new apps. You can run tons of free apps on it. The UNIX underbelly lets you do all sorts of things.. but you likely won't, unless UNIX means something to you (it's the primary reason I use OS X). It'll run fine for years. OS upgrades will likely cost you $30 every couple of years.
There are, of course, people who switch to Macs, hate them, and switch back, but, percentage-wise, that is rare. Most people who use Macs love them, which is why Apple has such a great consumer satisfaction score. People with Macs tend to love the computer itself in addition to what they can do with it. Any tech can break or glitch, but the odds are that you will love this. Unless, of course, you're predisposed not to.