As far as I know, there's really no limit...a teacher that attends a workshop gets something along the lines of 300 seats for their school (At school and for student home use). [
http://www.ptc.com/company/community/education/]
Do we have to re-register for the 2009 season? My brother and I are having difficulties trying to log in: we type in the login info and it doesn't deny it, but it won't load the client. I know my account might be a problem since I didn't register under the same email that was invited, but dunno about his.