http://au.wii.ign.com/articles/863/863040p1.html?RSSwhen2008-03-28_145800&RSSid=863040
For those of you too lazy to click the link, there's a Karaoke WiiWare game coming out in Japan this summer and they're aiming to have 20,000 songs available at launch, with an additional 1000 new songs per month.
Not something I'd play, but that's a pretty ridiculous number of songs.