I was in the same boat as you 2 months ago. I didn't find much on the net related to this lens so I went I bought it anyway.
Take a look at my flickr page. A good bunch of the birds shots are with this lens. I didn't shot much yet but it can give you an idea... BTW I'm just starting with birds so I'm not in the same league as some members here.
At first I was disapointed by it. Sure when you compare with 500 f/4 & 600 f/4 this isn't the same category. However the more you use it the more you'll appreciate it. I personally think it's great up to 380-400mm then it start loosing quite a bit of sharpness. 500mm is fine if you don't crop too much... I can crop to ~40% without seeing any problems at 500mm. But hey you pay for what it is. I paid 1400$ Canadian for it. I also have the 70-300VR. I think it's only 600$ Canadian now. You should consider it. It is much lighter, smaller and overall I think it's a better lens especially because of it's portability. With the 150-500mm you'd better have a good tripod and solid shoulders for long hiking
Mogur, I've checked your pelican set. I don't think that you would have gotten better shots with the 150-500OS in this case. 1/1000th @ f/9 would not get sharper with the addition of OS. I don't know if the AF accuracy (in servo mode) of the 150-500 is better than that of the Bigma
