You can learn all sorts of things by looking at energy in and energy out. PZTs produce lots of voltage, but at almost no current. The energy produced is usually next to nothing. There are multi-layer PZTs that can product lower voltage and higher current, but the losses are usually higher. There's lots of energy harvesting research going on, but it's usually directed at sensors and things where the power draw is brief and intermittent, or just extremely low to begin with. If you had a continuously vibrating source, you could attach a PZT to a resonant beam and maybe generate small amounts of power, but the impulses from typing don't amount to a hill of beans. BTW, if you had a conversion device that could generate enough energy from typing, you wouldn't want to type anymore. If you don't understand why this is the case, you *really* need to go back and understand that energy in vs energy out relationship. This is OT, but this is just a small part of the overall alternative energy schemes that so many people are looking at. Most of them are losers right from the start (the schemes, not the people). Go to Don Lancaster's Guru's Lair site and read his analysis' of various PV, hydrogen and alternate energy attempts. If you think hydrogen is a fuel, don your fireproof underwear before reading his stuff.
CH