General

@BobR: ohh, it all makes sense. thanks.

[quote=Subtly]what's the difference between the two. (membrane/mechanical)[/quote]
They use different switching mechanisms.

A "membrane" keyboard uses three large pieces of plastic (essentially the size of the whole keyboard), sandwiched together, one stacked on top of another. The top and bottom have contact surfaces "printed" on them that are kept separated from each other by the middle layer of plastic. At the spot under each key, there's a hole in the middle plastic layer which allows you to push down on the key, which pushes the contact surfaces together through the hole, making an electrical circuit which the computer can sense as that key having been pressed.

Since you're really just pressing two sheets of plastic together, there's no real "feel" to the contact, which makes it difficult to tell when you've pressed the key hard enough to be sensed by the computer. Because of that, most membrane keyboards have a rubber or metal "dome" added right below the key which has to be pressed until it "snaps" down and hits the membrane. This gives a better "feel" to the keypress, plus it acts to push the key back up when you remove your finger.

They're really cheap and easy to make, but as mentioned above, the contact surfaces don't last very long over many presses which can cause reliability problems.

A "mechanical" keyboard uses individual little electrical switches under each key, like a light switch on your wall. The contacts are metal fingers or discs which are pressed together when you press the key, making a very reliable connection which can stand up to many, many key presses over time. The switches usually have a metal spring which pops the key back up and opens the switch when you remove your finger, giving it a good "feel". Because of their greater complexity and materials needed they're usually more expensive to make.

What do you want this keyboard for? It definitely feels better to type on a mechanical keyboard, but it's not the clear winner for gaming. I personally don't care whether I'm using my Model M or my laptop keyboard when playing games. Oh and you could probably get a Model M for cheaper than that Razer keyboard. A more recent Model M will cost around $30 (Pre-Lexmark Model M's will cost quite a bit more.). You can also get a Unicomp Customizer, which uses the same switches as the Model M, for $79 new.

http://www.overclock.net/keyboards/491752-mechanical-keyboard-guide.html

"
Rubber Dome
Pros:
* Cheap
Cons:
* Contact pad wears out quickly
* Frequently used keys lose their tactile feel due to the rubber flexingPros:

Mechanical Keyboard
* Very quick snap back into rest position
* Don't necessarily have to bottom out to actuate
* Very durable - some are rated up to 100 million keystrokes but still go for much longer
* Virtually no degradation - the feel remains almost constant over the lifetime of the switch
* Replacement of a single switch is possible if one goes bad
Cons:
* Expensive
"

However, the article is biased.

what's the difference between the two. (membrane/mechanical)

One argument in favor of mechanical keyboards is that the mechanical switching action is more positive and responsive than a membrane style keyboard, for things that require quick response like gaming.

Also, the "feel" can be considerably different and is something that's a more personal choice. I prefer the positive feeling of my KeyTronics keyboard over the mushy feel of a typical membrane keyboard. (The KeyTronics is still a membrane switch, but has a high-force plastic dome in each switch which gives a much more "definite" feel to depressing the key. I hate the ones where you can't even really feel whether or not you've fully depressed the key.) Because of the more positive "feel" to them, mechanical switch keyboards may also allow higher typing speeds.

Mechanical keyswitches generally have longer lifespan than the typical membrane unit, so they're often used with office computers where they get hard use and you don't want to be replacing them all the time. They usually have way better liquid resistance as well. (I've actually cleaned mechanical keyboards by holding them under running water and drying them with a hair dryer. Membrane keyboards are usually destroyed by liquids spilled into them.)

Other than that, for general purpose use, there's probably not a whole lot of difference between the two except for the price.