With the 16 MP DX sensor 1 over 2x focal length is probably a better rule of thumb. At least for shaky old guys like me.
>Although likely not specifically related to your issue, a >rule of thumb on shutter speed to avoid "the blurs" >is to insure your shutter speed is equal to or greater than >your lens zoom. > >As an example, if I am shooting (hand held) with my Tamron >18-270 and I am zoomed out to 150mm, I insure my shutter speed >is higher than 150. > >That helps eliminate the shaking exaggeration that occurs at >higher mm.