As I've been playing I've run into a lot of features I think are "neat" or "well-done". This particular one falls into the "well-done" category, and into the category of "makes playability better for me according to how I use my desktop"
In short, I love the way the World of Warcraft play window is pretty much infinitely resizable, and in resizing the window, the whole game window graphics resize so you still see the entire play window no matter how small you make the size of the window itself.
This means that I can run my Instant Messenger client and have it visible while I play, without losing part of the play window under it.
This means I can have my Windows start bar as big or as small as I want it.
This means I can resize the window I'm taking screenshots of so I don't have to resize the image later if I need it to be smaller!
Oh the joys!
One of my Internet Pet Peeves is websites that expect to use the whole screen width no matter what resolution or screen size they're dealing with. I hate it when websites try to dictate to me that I, on my 19%26#8243; monitor, cannot have ICQ running and visible on the side of my screen at all times.
Thank you Blizzard, for addressing this pet peeve of mine without having even known me! ;)
PS: To resize your play window, hit 'escape' and go into Video options and check off the box for "windowed" mode. From there, you can click and drag on the corners of the windows as required for resizing/dragging.