As a new customer of a Cokin Grad ND filter(s), I look at this for inspiration! I hope my photos come out half as good as yours do. I'm under the impression that you have to wait for the sky to be blown out. I think in the next few days, I might try to get a stronger grad, or maybe a hard edge filter. My two soft ND grads arn't doing much for me. It's been real cloudy(like overcast) so I havn't had much chance to use mine.
Thanks. You can use the grad nd's at most any time. My two favorite times are sunset and overcast skies. During an overcast day you can use the grad nd to make some really stormy-looking pics. There's a lot you can do, you don't always have to wait for the sky to have a particular look. Have a look at *angelreich's gallery
Oh wow, thanks for the link. I'm going to try some more today. I haven't even gotten any photos I took with the new filters on my computer, so who knows what they really look like. It think I might need stronger filters though : (