It's largely subjective; the feedback of mechanical vs. membrane keyboards can certainly be measured objectively (i.e. pressure for key presses and snapback time), but it's just a matter of personal preference between the two (and I wouldn't consider the better feedback to be just a neat aesthetic benefit; it's the reason I bought it, not a bonus). My dad has always used an old clacky mechanical IBM keyboard but has no problem using membrane keyboards. I can use a membrane keyboard if I have to, but now it feels "mushy" after being spoiled by my Topre.

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...