I think I've come to the conclusion that I prefer the 35mm focal length over 50mm, so I had kind of gotten my heart set on the Nikon 35mm prime, but I've also heard good things about the Sigma, not the least of which is better bokeh and 2/3 of an f-stop (so even better low-light performance). Unfortunately, the Sigma is twice the price.

Have any of you tried it? Do you think it's worth it?