You may never have tried to play a file ending in "OGG", but you'll likely be using the software behind it soon. Google's new high-end VP8 video format endorsed by Mozilla and others is an open format video format that uses the long standing open audio format. The #2 audio player maker SanDisk already supports OGG in most of its players. Now OGG music will run without any additional downloads or plugins inside Firefox, Chrome, and many other programs, including Android cell phones.
This brings up the question, will Ogg take over where MP3 left off? Although it works on almost every audio player in existence, many other formats are lined up to take its place with dramatic space savings, support for surround sound, and other features, there's some strong resistance from Apple. Their devices use a drastically different format and likely will never support Ogg. Apple CEO is actively against the format, both for patent, technology, and of course his own interest in owning MP3's successor.
Hopefully Google's backing and the (so far) very strong success of open formats in determining technology standards will stand up to a legal assault by Apple.