I use my launch K3 about 4-5 times a week.
Since I don't like the weight of the case when I don't need the light I'd take the K3 out of the case. But then I'm putting it back in the case before the night is over. So on average I'm probably taking the K3 out of the case once every other reading.
Last night the light stopped working
Off to contact Amazon CSR for a replacement.
-edit, Purchased September 10th 2010 so it was still under warranty. CSR is shipping me out a new one. Woot!