Alright... here's a killer for you: I got the Panny 45-150 for Christmas after giving my 45-200 to my niece. And then I couldn't resist picking up the Oly 40-150 for only $99 earlier this month. Hey, sometimes Panny lenses work better on Panny bodies and Oly lenses better on Oly bodies. So I have both. But I have had exactly zero time since Christmas to go out and test either. Ain't that a kick in the head? I can tell you build quality is fine on both. The IS switch is no longer on the outside of the Panny 45-150, the way it is on the 45-200. It's activated via the menu only. Zooming/focusing is also quieter than with the 45-200. The Oly lens is lighter, since there's no IS. I'm kind of frustrated that I can't tell you more. But, frankly, I don't think I'd sweat it if I were you. If I had only a Panny body, I'd get the Lumix version. If I had only an Oly body, I'd get the Zuiko.