Ashley
Ah I didn't know you could just rename to .zip like that :)
I use Git for version control and it looks like it's including the .git folder in the backups. Committing, then backing up the commit, then recommitting ad infinitum must have caused it to exponentially grow.
I can't imagine what Subversion would be like with all the nested .svn folders :O
Not sure what the solution would be - not to backup hidden folders?