The 10 billionth iTunes download is fast approaching, and Apple's offering up a $10,000 iTunes gift card prize to one lucky winner. That winner will either be the downloader of the 10 billionth song, or the person who submits the first non-purchase online entry form
immediately following the download of the 9,999,999,999th song.
Based on those rules, considering there are still over 100 million songs to go, it makes no sense to try to enter at the time of this writing. It's totally based on when you enter, not some random drawing of entries, unless you happen to tie for the 10 billionth entry.
Last year, Apple had a similar promotion for the 1 billionth App Store download. However, they must value App Store downloads much more than iTunes downloads, as that promotion included a lot more than just the $10,000 iTunes gift card: the lucky winner collected an iPod Touch, a Time Capsule, and a MacBook Pro, as well.
Apple calls it "one huge milestone for music," and it is, but Apple hit a bigger milestone much earlier. In 2008, iTunes became the number one U.S. music retailer.