Can you say more about what problem those $250 keyboards are solving? I guess I never find myself with issues where keys don't register or anything like that, even with a $15 crapola one. (Wireless ones, however, are a different story.)
* The feel of the mechanical keys is fantastic. There's much more feedback; keystrokes make a nice subdued "schlock" noise. The backspace key sounds like the sound from Mario games where he does that spinning landing thing on a baddie.
* Easily swappable keys; my WASD are swapped for the purple arrow keys they come with, and my Esc key is a nice dangerous-looking red.
* LEDs are built into the keys they're for. Not a killer feature, but pretty slick.
* Flexibility; there are dip switches in the back for various tweaks such as swapping Ctrl and Caps Lock on a hardware level - they even provide keys to switch out so that the new Caps Lock key gets its LED.
For something I'll be typing on for many hours a day it's a worthy investment.
Membrane keyboards are cheaper to make (because most people don't care) but have less tactile feedback and are less reliable. Mechanical keyboards are more expensive to make, but are much more durable (keys will not wear out) and have quicker key snapback. Lack of n-key rollover could also be considered a defect of inexpensive keyboards, although it's not a common hindrance to casual typers.
More information: http://www.ergocanada.com/ergo/keyboards/mechanical_vs_membr...