I hate to be heretical but I doubt that anyone can judge the sharpness of a lens from a webposting at 72 dots per inch (although I like your shot Peter.) My guess is that almost any modern lens will give a photograph that's as sharp as the web can show, provided the subject and/or the camera is not moving. In fact (said he, donning his flame retardent suit), I'd even guess that almost any modern lens is sharper then we can discern in a hard copy, given the effects that occur because of camera movement, even when the camera is on a tripod.
I've done tests of the macro capability of the 28-105 against my 60mm Micro Nikkor. I did the shots with tripod support. The results were as you might expect, the Micro Nikkor is much sharper across the entire frame. The zoom lens has a relatively small center area that is sharp and the image gets progressively softer toward the edges of the image frame.
The 28-105 shouldn't be your first choice for macro work, but having the macro is handy when you're travelling light. Be sure to keep your subject in the center 20% of the image frame if you want it to be reasonably sharp.
If you plan to take pictures of postage stamps, then get the 60mm micro nikkor. If you plan to take pictures of flowers, then the 28-105 nikkor is very good. As BJ pointed out, the lens is very sharp in the middle and gets progressively softer toward the edges. Well, if you take alot of flower pictures like I do, the macro of the 28-105 is more than sharp and it produces great pics like the one posted on this thread.