One of my favourite features in Lightroom 2 is the Lightroom Graduated Filter. It's fantastic for fixing photos where your sky is blown. It's quick, easy, and does a great job.
I've put together a quick little video showing how to use it. The end result is quite punchy and I'd tweak the photo a bit more if I was making a print, but it shows the graduated filter effect quite well.
Also wanted to point out, the video compression makes the sky look a lot worse than it actually is. It isn't actually that blotchy. :)
Here's the original image with no graduated filter. It was a bright, sunny day, and you can see the sky is blown out.
Here's the end result after I've applied a graduated filter in Lightroom as shown in the video. I also punched up the color with the Lightroom Vibrance setting.
Try the Lightroom Graduated Filter for yourself. If you haven't used it yet, I think you'll be surprised how quick it is to use and how well it works.