Interesting question. Here's how I see it at first glance.
The usability of a window tiling practice is tied essentially two two things:
- Current resolution
- Type of applications opened
The higher the resolution the more such a feature may make sense. In today's world where resolutions of 1440x900 and higher are quickly gaining ground as mainstream, there may start to be a practical reason to tile windows in such a way. Consider that not so long ago we were all comfortably using 1024x760 and that today we have gained ~400x200 pixels without that meaning much anything else other than more space for one application screen. One must wonder, could I make use of the added space more efficiently?
The type of applications being used may also make a significant difference in evaluating the usefulness of such a feature. It's a fact that screen real-estate is often misused without we ever realizing it. It's a deeply ingrained habit that we overlook. Consider your habit of firing up a text editor. Do we really need to see 170 characters wide of a text file, especially when we have a convenient wordwrap feature at the click of a mouse? Conversely, a browser or a full blown integrated development environment may need that space. Although I'd be tempted at reevaluate my 1440x900 browser window. Right now looking at this website I have around 400(!) pixels of wasted horizontal space.
My verdict would be like this:
It's quite possible that anyone swearing over a window tilling usage pattern may be part of an "enlightened elite"; Those who were able to overcome deeply ingrained computer usage habits that we tend to overlook. I'm pretty sure they don't support it on every case, but swear by it on many cases simply because when we really look at our screens, we get the shocking revelation that for many common tasks we have been very wasteful.
On the other hand, we cannot deny that other factors come into play. Operating systems like Windows Vista and Windows 7 are by default screen real-estate hogs with their fat title bars, not very friendly adjustment to smaller fonts and a general feeling of "big and fat everything" where it's easier to make things bigger than it is to make them smaller.
I'd say, there's room for window tiling even in here. I just tiled this website with my console and a text editor to prove that much to myself. And it dawned on me I just did what would need 3 monitors to do without any significant loss of productivity. But by no means does this mean I can do it all the time and with every application. So, I'd say keep those tools handy and become aware they are there for you to use. You may as well find you'll get to learn to use it more often than you first thought.