If you’ve got a massive music library, better think twice about syncing it with iTunes Match as the maximum size of an iTunes library in the iTunes Match beta is 25,000 songs, according to “Cult of Mac” (http://macte.ch/jGYsQ).
Assuming a library in which song is an average of 4 minutes long and compressed in CD quality 320kbps, that basically means the upper limit on a library is a size of 250GB, the article notes.
iTunes Match will be available this fall for a $24.99 annual fee. Music not purchased from iTunes can gain the same benefits by using iTunes Match, a service that replaces your music with a 256 kbps AAC DRM-free version if Apple can match it to the over 18 million songs in the iTunes Store, it makes the matched music available in minutes (instead of weeks to upload your entire music library), and uploads only the small percentage of unmatched music, according to Apple.
