I almost didn't buy this lens, but right before I left for my trip I decided it would be worth it and thank gosh I did! I did a safari in South Africa and in the wild, of course, animals don't come up to your car, but with this lens I was able to shoot close up photos of lions that were hard to see with the naked eye, as if I were right next to them. I bought the NEX 5 for the high quality video and this lens made it a real joy to shoot video. I just returned home yesterday and now I have so much video that I would never have taken except for the fact I could get so close up! I love the auto focus function. It exceeded my expectations for performance in videos, especially given alot of negitive stuff written in reviews I had read.
That said, it is expensive and had I not been on a safari, I probably would have been fine with the lens that came with the NEX 5. Also, within a couple days two specs of dirt or something appeared on the inside. This has luckily not affected the images that I took, but for good measure I am going to test the Warranty since dusk inside the lens is obviously not my fault and for this price that shouldn't happen, and I assume that it will be taken care of by Sony since I only bought it less than a month ago. However, if not, I will update this review and let the world know. Also, I am planning to buy a protection lens filter to over lay over the lens so that I don't have to be so parinoid about scratches.
Overall, I love the NEX 5 and for my trip, knowing what I know now, this was a great accessory despite the price. If in doubt, I say go for it, you will have the best lens for the size and it will last you along time!