I've done it a few times.
The USB flash drive gets slightly warm to the touch.
The install takes roughly half the time as from a DVD. (That's with a cheap, low-performance, flash drive. I guess that the speed comes from the low reading latencies, not the streaming data transfer rates.)
At least here in the US, 4GB USB drives are readily available for $7.
Even if the drive's lives were shortened (AFAIK, they are not), would it matter?
To coin a phrase, just do it.