(I should also point out that if your keyboard has seen so much use that its key labels have worn off, a keyboard skin is also a relatively inexpensive way to figure out which key is which.)
But not all keyboard covers are equal. Over the past few months, I've been taking a few for extended spins on several different laptops. It turns out that despite their apparent similarities, keyboard covers actually differ in a number of ways, including appearance, fit, and the feel of the material itself.
(Note that because Apple has recently settled on a standardized keyboard design for all its products, a keyboard cover designed for Apple's current MacBook line should fit the MacBook, MacBook Air, and MacBook Pro, as well as Apple's keypad-less Wired and Wireless Keyboards.)
iSkin ProTouch FX Keyboard Protector
iSkin's US$35 is unique in that the company has treated the keyboard skin with an anti-bacterial agent; iSkin claims this "inhibit[s] the growth of odor and stain causing bacteria." In addition, rather than using a clear design, all ProTouch FX models are made of semi-transparent silicone with solid-black keytops and white key labels; you can choose between clear, blue, or pink for the silicone color. These black-and-white keytops make the keys easy to read, but they have one major drawback: If your Mac notebook has a backlit keyboard, the ProTouch FX blocks this light completely. (Although there's at least a tiny window that allows you to see the capslock-indicator light.)
The ProTouch FX fits a MacBook keyboard well, but I was disappointed by the feel of the cover. If I pressed directly in the middle of each key when I typed, the ProTouch FX worked fine. However, the sides of each individual key cover are more rigid than on any other skin I've tried--rigid enough that if I pressed a key off-center, the key often didn't register. Over time, I was able to adjust to this behavior to some extent, but never completely.
KB Covers Checkerboard and Clear Keyboard Covers
As you might infer from the company's name, KB Covers specializes in keyboard covers, producing basic, protective covers for every Apple keyboard, as well as foreign-language covers, covers with keys labeled for specific programs (for example, Photoshop or Final Cut Pro, or World of Warcraft), covers with large-type labels, and even for those learning to touch-type.
I tested the MacBook versions of the company's and , each $25. Specifically, I tested the Ice model of the Clear (model CV-M-Clear), and the Checkerboard version made of clear silicone with black keytops and white key labels (model CB-M-CB). The Clear is also available in transparent blue, green, pink, and purple silicone. The Checkerboard also comes in clear silicone with white keytops and black labels, and in clear silicone with black keytops and white labels.
Both covers fit the latest MacBook-style keyboards well, although, as with the ProTouch FX, the sides of individual key covers are fairly rigid. I didn't have nearly as much difficulty typing on the KB Covers models as I did with the ProTouch FX--the KB Covers covers didn't cause me to mistype--but both the Checkerboard and Clear gave my keyboard a noticeably different feel.
The differences between the two models are minor. Like the other non-clear covers here, the Checkerboard's solid keytops block keyboard backlighting; the Clear lets you see the keyboard's actual keys. Also, I found that the Clear was slightly more flexible, likely because of the lack of labels on each key, compared to the Checkerboard. The downside of this flexibility is that the Clear's silicone occasionally got stuck underneath the edge of the space bar, preventing it from recognizing key presses. This didn't happen frequently, but often enough that I noticed.
Moshi Clearguard
Moshi's $25 is the only cover I tested not made of silicone; instead, it's made of thermoplastic urethane that's 0.1mm thick--by far the thinnest keyboard cover here. This material and its thinness provide two immediately obvious benefits. First, the Clearguard is almost completely clear; when placed on a MacBook's keyboard, you can barely even see the cover, and if you've got a backlit keyboard, that lighting shines through at full brightness. Second, although you do notice the Clearguard while typing--it gives the key surfaces a slightly tacky feel--the overall feel of typing is affected less by the Clearguard than by any other keyboard cover I've used. Compared to a bare keyboard, it takes approximately the same amount of pressure to activate each key, and the tactile response you get is nearly unchanged.
Although I haven't used the Clearguard long enough to determine how its material will hold up, over time, compared to a thicker silicone cover, after a month or so of use it's become my keyboard cover of choice.
VisiKey VisiSkin
VisiKey specializes in easier-to-read keyboard solutions, both for those with visual impairments and for people who simply want to reduce eyestrain from reading tiny labels. We , but the $10 is a silicone cover designed specifically for Apple's latest keyboards. What makes the VisiSkin different, besides its low price, is that it's white with huge, black key labels, making it easy for those with poor vision to identify most keys; the large type is also useful in dimly-lit work environments. However, there are a few labels that don't get the huge-text treatment: alt/option, enter, the arrow keys, and the "shifted" behavior of 1 through 9 (in other words, !, @, #, and so on).
Although the VisiSkin's key corners are squared off, rather than rounded like the actual keys underneath, this never affected my typing, and the cover fits well. Of the covers I tested for Apple's current notebook keyboards, the VisiSkin was the thinnest and least obtrusive among the silicone skins. Note that while the VisiSkin fits all keyboards using Apple's current keypad-less design, the key labels are for the original MacBook's keyboard, which means that the labels for special F-key functionality (volume and playback controls, for example) are on the wrong keys. Also, like the ProSkin FX, the VisiSkin blocks keyboard backlighting.
Macessity Keyboard Cover for MacBook Pro
If you've got an older MacBook Pro--a pre-"unibody" version with the older, non-chiclet-style keyboard--Macessity's $15 is a good bet. Made of "clear frosted" silicone, the Cover lets the MacBook Pro's backlit keyboard to shine through, although the frosted appearance does give your keyboard a hazy look. The back side of the Cover is slightly tacky to keep the Cover in place, and the silicone is thin enough that it doesn't affect key feel much. A nice touch is that the bottom edge of the Cover is long enough to extend over the edge of the palm rest in order to help keep crumbs and other detritus from slipping under the Cover.