I have the 580EX and the Better Beamer. No doubt using the fill flash improved the quality of photos and adds a little "tone" to photos. I never could quite get the settings right for the Better Beamer and sometimes make the photo look a bit "over flashed". I guess more practice is needed.
I only really used flash in the United States where most of my birding was done by car and therefore easy to throw some more gear in the trunk. In HK where I am getting in buses and ferries and walking long distance, it's too much to deal with carrying the flash. But if you are stronger than me, it's worth experimenting with flash.
