I concede that the range of a RF keyboard can be very variable. It depends on the transmit/recieve antennas, the RFI in the environment at that frequency band, and the modulation (e.g. single freq or spread spectrum, AM/FM, etc.) However, I am not really sure why "line of sight" would be a problem. Even if you're a crackerjack touch-typist running some ultrastable variant of 'nix, you'd want to be able to see the screen to be sure you were at a command cursor rather than some error massage or dialogue; and even if you have the kind of mind that can play fifty games of chess blindfolded, a mouse *demands* a direct view of the screen: imagine that it got jostled a fraction of an inch, and the cursor wasn't precisely where you left it. You could close a window you thought you were minimizing to reveal the window behind it. (and if you'e not in a GUI envirnoment, why use a mouse?)
"Line of sight" in this context, is only important in a very strict sense: if a pile of books/papers , a desktop speaker, or the edge of a table gets in the way of an IR signal (Infra-Red, or a wavelength of light lower than the human eye can see), it can stop the signal cold -- though sometimes you get helped by a lucky beam bounce. RF (Radio frequency) however, penetrates such minor obstacles fairly easily. You don't have any problems using a radio or walkie-talie indoors -- they's be pretty useless if they were line-of-sight.
While it might sometimes be useful to submit commands from the next room (e.g. to operate a VCR/cable box remotely), it's rareiy useful to operate a computer blindly. RF (radio) remotes *can* operate through opaque walls -- that's why garage door openers are generally RF, but car door remotes are sometimes IR: it's convenient to have you indoor garage door reciever respond despite several laters of opaque, IR-absorbing or refracting glass, wood and steel, but it's not quite as useful to unlock your car door when you can't even see your car (or, for that matter, to open any accidentally matching car in fifty meters or three stories of a parking garage)
If RF has a drawback, it's a lack of security. IR *can* be read through windows, if someone is determines, but the same penetration that makes a RF signal so convenient for the user, also makes it convenient for an eavesdropper. Do you care? Probably not -- but a security conscious person should realize that any would-be eavesdropper would probably be using an antenna that was thousands of millions of times as sensitive as the one that comes with the keyboard/mouse (such antennae can easily be built from simple wire and a Pringles can and/or paper plate and aluminum foil -- not because such antennas are so great, but because the usual keyboard recieve antennas suck -- and "decibels of attenuation" is a logarthmic scale. Heck, a $20-50 Yagi array or RF amp would let an eavesdropper sniff passwords of key strokes for blocks or miles around -- or remot control your system, unless the RF keyboard/mouse uses good encryption, which few do)
Sorry. I know this isn't the usual tone for this forum. I usually keep my mouth shut. I thought these basic scientific principles might help anyone considering *any* wireless purchase, and there seems to be a great divide t between the many Anandtecher's to whom this stuff is second nature, and those to whom it's a total mystery. I'll crawl back under my rock now.
It can bounce right back up. LOL 
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