I've always found that straight b&w conversions (Ctrl + shift + U) come out very flat and lack contrast.
So, for the first version I used the channel mixer (tick the monochrome box in the bottom left corner), then I played around with the colour sliders to get a pleasing effect. Following that I used the contrast/brightness tool and finally used the sharpen filter. Probably no more than 5 minutes work at most.
The second version was rather more labour intensive. Start off with two copies of the image. Using the channel mixer and contrast/brightness tools (not the filter at this point), I converted each to monochrome, then adjusted one image to get a sky I was happy with and the other to do the same with the foreground.
The two image were then layered over each other and a gradient was used to blend between the good foreground and good sky. After that, it was just a case of using the dodge and burn tools to tweak the image into what you see now. The last step was to use the sharpen filter. Overall, that one probably took 20-30 minutes. The magazine I got the step by step from (Dec 06 - Digital Photo) reckons it's possible in 15 minutes, but this was the first time I'd tried it the method so I was a little slow whilst I found all the tools.
Hopefully no one gets the idea that I'm some sort of PS whizz, I'm not. All I've done here is follow a set of tutorials from a magazine. I did once used to do a lot of real b&w stuff in a darkroom, so I guess I understand the theory behind what I'm trying to achieve using PS. For a first attempt using the second method, I quite pleased with the end result, though looking at the full sized image I was working on, I can quite easily demonstrate the more ham fisted moments.