Ok how about PHP. Look at the metoric rise in usage it has had over the last year or two. Open source has been in the news that long. This is in use on well over a million servers worldwide and growing and replacing Active Server Pages. I think this is a very viable flag to hold up for this argument. I personally have been using php for over a year and I love it and recommend it to every web developer I know. And 100% open source. As the old commercial said "Try it, You'll like it, Hey Mikey";).