We are generally aware that whether RO/distilled or various amount of mineral does effect espresso extraction.
When I was at the MANE coffee conference I was talking with someone about nordic roasting and their quite different profiles. He said that when he visited that area that the local water had no mineral content and the coffee tasted much better/different there when brewed than when he brought it home and tried it with water with more normal mineral content. In a tweet from the Nordic Roasters forum going on now there was also mention of how much roasting is specific to the water being used to brew. So I'm starting to wonder at least at the extremes that roast profiles do matter with water being used. When I get a chance I'm going to try a couple nordic roast profiles and try brewing with different water extremes.

We have generally low mineral content here in Asheville (~30-40ppm) and I have found good success with very light / low development time roasts.

Water chemistry is key to brewing beer (http://www.byo.com/stories/article/indi ... your-water). Sulfates accentuate bitterness from hops, pH can effect efficiencies, etc. It wouldn't be surprising to me if they played a part in extraction and definitely in taste.