I bought this lens to be used on a Canon 6D and to replace my 24-105 f/4L IS USM and 70-200 f/2.8L IS II USM on a trip to Peru. I would have loved to have my L glass, but we were trekking the Inca Trail to Machu Picchu as well as many other treks and travel around the country so weight was a very big issue. I purchased the lens well in advance of the trip to be sure I was satisfied with the picture quality. It is a fuzzy line whether to take the best glass or to go light. I would be lying if I were to say there was never a time I wished I had my L's, but overall I was very satisfied with the photos I came away with.
I loved having the zoom range without having to change out lenses constantly. I was able to capture wide landscapes and urban buildings and then quickly capture a bird, or close-up of my kids. I did find that if I did not stop down a bit throughout the zoom range (f/8 - f/11), I noticed some vignetting in the corners.
A couple annoying things in my opinion. If you are used to Canon, the backward zoom ring rotation drove me bonkers at first. I did get used to it after a few times out, but it can still cause someone to miss a shot in a pinch. The other item for me is that the zoom ring on the Tamron is the outside ring and focus ring closer to the camera...also opposite to my 24-105 where the zoom ring is closer to the camera. With the zoom ring being closer to the hood on the Tamron, it is difficult to rotate the zoom without the lens hood turned out. I usually store my camera with lens on and hood turned toward camera for lower profile, so it got in the way when I would pull the camera out for a quick shot if in my bag. Most of the time on the treks this was not an issue since I had the camera in my hands while trekking.
All in all, a very good lens for travel. I will still use my L glass most of the time, but will not hesitate to throw this Tamron in the bag when trekking or just traveling in general.
A year later: Wanted to come back with a little update. I have had this lens for a year now and I find myself leaving the L glass at home more often when going on a hike or a trip even. I have printed several pictures for my home and office (some from Peru trip and others from day hikes and camping trips in my home state of Utah). Most of my prints are 20"X30" and one would be hard pressed to pick out which prints are from this lens or from my 24-105 L.