The Canon 70-300 DO is a lens that often gets picked on. They say its soft, the bokeh is funny, it has low contrast and its overpriced.
A lot of it is true. The bokeh is kinda funny looking. At 300mm it is somewhat soft and its definitely overpriced. The contrast isn't up to L snuff, but it didn't seem lacking to me. Besides, contrast is easy enough to fix in post.
However, for some people it may still have its place. It is reasonably light, but more importantly its extremely compact. Furthermore, it may pale in comparison to super telephoto primes (or the 70-200 for that matter) but with a little post processing, some judicious sharpening it can produce images good enough for web viewing or even small/medium prints.
On Sunday, we went for a walk around Kelley Park and the Palo Alto Duck pond. I brought only the 70-300 DO on a Rebel XSi.
I had to stop down to f/8 and it was mostly static shots that worked out but I still got some decent images.