I know we're mostly natural light folks here, and that's what I'm most interested in learning to do well, but I have REALLY been enjoying this CreativeLIVE course on using ETTL flash, and so I tried a before/after shot of Micah today, one without flash and one with flash in the same spot. The first shot was a bit OOF and he's not smiling, so it's not superb; but that aside, the light difference is cool. The flash shot just highlights his eyes so well and gives such nice light overall. It's definitely something I'd like to learn more of, especially for shooting outdoors to underexpose some of the background to get rich blue skies and still really light the subject well.
Here's the web site for the guys who are teaching the course; they use ETTL all the time and have some fantastic images!
TriCoast Photography LLC