Although they won't admit it, one of the big reasons corporations use Microsoft Windows is the ease with which they can spy on employees thru hidden keyloggers, etc. They claim they are legally liable for employee actions, etc. so they have the right.

On linux, it would be hard to do without modifying the kernel. I can't remember where I saw it, propbably on freshmeat.net, but a keylogger kernel patch is available for linux. You would have to be nuts to install it on your own machine, because who knows if it could get sent out over the network.

But Perl itself will never be able to do it, unless you stuck in 1 application all day long.

A hacked X server may be able to do it in X windows.

If I were to be put in charge of developing such a keylogger, I wouldn't waste time with platform specific software issues, I would go right to the source....the keyboard. Hire a keyboard company to make keyboards that emit small radio signals for every key typed (along with a keyboard id), and have a central collecting receiver. Ooops.....the men in black are pounding on my door, I think I just let the Tempest out of the teapot. ;-)