How Reliable are USB Memory Keys?

quecojones asks: "I've been thnking about getting one of those IBM memory keys. IBM's device seems a bit expensive, but I've found a few others made by JM Tek and M-Systems in a variety of sizes (16MB-1GB). They're suposed to work with Windows [98|ME|2K|XP], MacOS, and Linux. Just how reliable are these things? I figure they'd make a great little backup device. I could use one of these to keep my PGP keyrings, my PasswordSafe database, and a few other files. Why aren't these things made by other companies? It seems like a perfect floppy replacement. Another thing is, can I boot a computer with one of these things? If I get one of the larger ones (512MB-1GB), could I just install Linux on it and boot from it. It would make trying out different Linux distributions a lot easier. Jus try each one out on the USB drive to figure out which one you prefer and then install it on the HDD."