You might think that those green "retweet" buttons you see across the web (including on this site) are controlled by Twitter, but they're actually the key component to TweetMeme, the tweeted link aggregator. And now that key component is under attack by the new service ReTweet.com.ReTweet.com, which launched this week looking shockingly similar to TweetMeme, now has a contest that will reward $10,000 to a blogger that installs their retweet button on their site. While they don't explicitly call out TweetMeme's button, they do have this very blurb featured prominently on the site: "Add the Real Retweet Button to Your Website!", which of course implies that the TweetMeme retweet button is not the real one.