I bought two new BionX PL-350 systems at a 50% discount on Craigslist (keep your eyes open, it happens). They have been performing great for me. I live in a somewhat hilly area, and have tested the system quite a bit. First abuse - on a relatively new setup, I rode my BionX equipped Xtracycle on a century, and it made it 99.6 miles before the battery finally died (I did this by using regen, and pedaling on the downhills) - http://web.mac.com/zorbathegeek/Cadillac/2009.html#22

The second test was winter/all-weather resistance. This test it did okay in (i.e. riding t work regardless of weather, in a town that salts the roads till they're white). For the first couple of months the system did fine, but after a while the computer started locking up, and then it was more or less useless until spring. I later found out that if the hook-up for the battery is wet, it reproduces these same symptoms, so I'm trying again this winter and will be covering the bike when it get's wet out.

The third test is my current mode of commuting, which is with my wife riding on the back of the bicycle, and climbing two hills with a 8-10% grade. Without the assist, I could ride up on road tires at around 7 MPH, but it was very hard. Now I put the snow tires on with the motor, and I can ride up the hills at 13 MPH with moderate exertion - that is a huge improvement.

So, I would say that while the PL-350 has its limitations, if you treat it right it is a down-right resilient beast.