Mine was on for more than 10 days at a stretch and then it started getting slow last night. At one point it became unresponsive - dark screen with lighted capacitive 4 buttons at the bottom of the screen. I pulled the battery and restarted it.
I faced soem slowness this morning too. I again pulled the battery and restarted it. I had to uninstall Android Assistant which was running all the time in background and hogging resources.
So once a week is good at least for now for me.