Lately I use Musescore for my harmony lessons, but I didn't know about the new service in http://musescore.com/ to easily upload music score and share them over the Internet.
The site is still in alpha version, but it works pretty well already. As a test, I got the Harmony exercise for this week and (from within Musescore itself) I uploaded it to Musescore.com in a matter of minutes (http://musescore.com/score/3533). From there you can listen to the composition and download the score in different formats: MuseScore, PDF, MusicXML, MIDI or even MP3. Cool!
EDIT (24/5/2011): In the end, after a few corrections suggested by the harmony teacher, the final score (which was played together with the compositions of other students on 20/5/2011) is here.