I think it's safe to say that the results I get from this lens are not going to be great without ideal natural settings. That's OK - I knew what I was getting into when I bought it.
Here are some samples; I made some slight edits to the first one to crop it so that there's not so much sky in the photo (I did a horrible job framing it). The picture of the coloured leaves definitely turned out better than the other 2.
Here are two photos - the original, plus an edited version where I tried to clean it up a bit to bring the lamp post into better focus. I think to fix it I'd need to work with the RAW file in Lightroom (or, basically any tools more robust than what Flickr provides).