Summary: I considered the Canon EF 100mm f/2.8L IS because it's essentially the gold standard for its kind, but went with the Tamron SP DI Macro based on the numerous positive reviews. VC image stabilization adds that wiggle room in shooting at lower shutter speeds, which puts it in Canon's class in that regard.
Excerpt: I am just starting to work with this lens. So far the lens is nice and sharp. The lens seems well built. The focus speed is fine for what I have tried. My initial shots were made on a tripod so I do not have much to say about the vibration compensation yet.
Pros: Easily Interchangeable, Fast / accurate auto-focus, Lightweight
Summary: This is my second lens, after a Tamron 17-55mm, and it's beautiful. I borrowed a Canon 100mm 2.8, and this has the edge, with better blurring and quieter optics. I'm far from an expert, but am quite a happy customer.
Excerpt: Got this lens last week and took it out for a spin. It fills out my lens armory perfectly. A great portrait lens and it also gets me in close for those abstract natural landscape forms that I am so fond of. It is light yet seems to be well made. It's not cheap at $ and change but I know I will get a lot of mileage from it. There seems to be a strange frame creep situation going on however when I use focus stacking techniques on manual focus.
Pros: Lightweight, Nice Bokeh, Strong Construction
Summary: This is my new favorite lens. I actually bought it mostly for macro (which it does beautifully) but what I'm diggin' most is using it for a portrait lens. It has a really nice bokeh (such a fun word) and the compression is so flattering to the facial features. Feels solid, focus speed is more than acceptable and consistent. If you're on the fence, buy it.
Excerpt: This is my first Tamaron lens and I love it. Between work and home I have access to 15 Nikon lenses and 2 Tokina wide angle zooms. This lens is easily one of my top lenses. I was going to go wth the Nikon 100 macro until I started reading the reviews. The Tamron 90 is sharp, quick, quiet, and the VC works great. No regrets.