You know the retweet button you see on content spread throughout the web? You can thank TweetMeme for that. Long before Twitter's new Retweet functionality existed, this button was the way to share on Twitter. And it still is for content not on twitter.com. But now it's time for TweetMeme to think about making money. And they've come up with a way that people are either going to love or hate. At our Realtime CrunchUp in San Francisco today, TweetMeme founder Nick Halstead has unveiled AdTweets. As you might expect, this involves ads that appear on your site — but with the addition of a retweet button. Yes, you can also retweet these ads just as you would any piece of content.