The 18-200VR has a terrible Internet reputation, but it's really quite good from about 24-100. Its weakest point is wide open at 200mm, and if you compare that - especially in the corners - to the center of the 105 Micro, it won't be much of a contest. And the famously sharp 105VR is probably the worst of the mid-range macro lenses, believe it or not. As near as I can tell, the Tamron 90/f2.8, Sigma 105/f2.8 HSM OS, Zeiss 100/f2 and even the previous 105/f2.8 AFD Micro-Nikkor all outperform the 105VR, by at least a small margin.
_____ Brian... a bicoastal Nikonian and Team Member
My gallery is online. Comments and critique welcomed any time!