No, this thread is not about pickup lines.

Does anyone here have experience with piezo pickups, PET pickups, similar contact microphones and especially portable amplification for such pickups?
They tend to be pretty special and picky, such as requiring very high input impedances.
Non-portable microphone amps that work well with such pickups are also welcome. (great High-Z inputs)

On a related note, I'd love some input on various brands of pickups.
The target application is a contact vocal microphone, but different pickups would be also nice to have - say, acoustic guitars.