I keep mine on, but every 3rd day or so, I power completely down and back up. I recommend doing this.
I also find running Advanced Task Killer, and 1Tap Cache Cleaner once a day to be helpful.
YMMV.
There are people that will tell you to let the Android OS itself manage memory. But this is the real-world with lots of different programs from different sources. They aren't screened like they are on the Apple OS before making it to iTunes App store.
Both actions, periodically rebooting, and between power-cycles running Advanced Task Killer and 1Tap Cache Cleaner has kept my MT running responsively.