I have been using this lens few months back, mainly for shooting birds. IT is not ideal but I don't want to fork out a lot of money only to realise I am not that interested anymore. Ok. Here are my observations.
Build wise it is not bad. Quite comfy to handle. Its auto-focus is good, doesn't hunt in evening light conditions. Night time depending on subject it may hunt, but this is the same for many othe lens so not an issue.
It has no IS and the effect is obvious. It shows up. Or maybe it is my hands or skills that is shaky. Anyway most will advise you to use a tripod if you are using at 300mm for wildlife. Do that and it should be fine. I have my miss shots but my better shots are really pretty good (for the price of this lens)
As a side note, the macro function is not a real macro one only 200-300mm can activate and I heard the ratio is 1:2 instead of 1:1 in ideal macro lens.