The Singh Ray Blue n Gold is a great filter to have in your bag. I don't use it often, as I don't get out to shoot landscapes (or travel) near as much as I'd like to. And sometimes when traveling I get stuck with crappy conditions when shooting landscapes; I just don't have much choice. It's those crappy conditions that I find the Singh Ray Blue n Gold filter earns its space in my bag.
It sure is a niche filter. When it works for a scene, it works great. I have the Singh Ray one and have taken some interesting shots. Its not a every day shoot filter.
it is simply an effects filter that in certain situations has a pleasing effect or as was mentioned a less then. i owned one for a short time. didn't fit my uses.
Btw, the Singh Ray tips on using and post-processing of images captured with the Blue N Gold are helpful in using/understanding this unique filter. There are a couple of small links located about half-way down the page: http://www.singh-ray.com/goldnblue.html