Why guiminer is using different amount of GPU each time I restart my copmuter? Why guiminer is using different amount of GPU each time I restart my computer?
I'm running guiminer-20121203, NVIDIA GeForce GTX 670M, poclbm.exe with flags  -s 0.005 -f 60
What I noticed was, it was 35Mgash/s with 75% GPU usage. And after I restart my computer, it became  50Mgash/s with 100% GPU usage with the same flag settings.

Also, before when I tried only with flag -s 0.010 it utilized 100% GPU, but without restarting computer, using flag -s 0.011 reduced GPU usage to 60%.

What's going on??
Other applications can alter your GPU settings not just guiminer.

If you take a read over this question here it may reflect a similar circumstance which is causing a variable hash rate on your hardware. Without knowing your exact usage of your computer though I cant say for sure.