USB Flash Drive Power?

[R]

I have a couple of Lexar FireFly flash drives that I've been
happy with. I wanted another to put the OS X 10.6 installer
on and decided to go with a Lexar VE this time as the other
one was out of stock. When I plugged it into the keyboard I
was suprised to be told there was insufficient power for it.

Should I be surprised? The two FireFly drives work fine if
connected to the keyboard, which is quite convenient.
I can use the new one if it's plugged into the monitor, but
I'd rather use the keyboard USB slot.

The VE is slow to write to, so it doesn't look like the
higher power requirement is adding to performance.

Here's the thing, if you're interested:

http://www.lexar.com/au/jumpdrive/jd_ve.html

It's quite nice physically, but I wouldn't recommend it.

A couple of other questions. Are flash drives suitable for
medium to long term backups? How would one know the
power requirements in advance?

Thanks!