Does using personas / themes count towards my download limit?

Yes.

Only downloading a file (theme or persona) does account to your download limit.

Once you've download a persona (or theme) then using doesn't account for extra download quota. Additional Personas are not stored on your computer,so if you switch a persona then the new persona needs to be re-downloaded from the (getpersonas) server. A theme is stored on your computer, so switching themes requires no extra download.

Thanks cor-el that's really helpful to know :)

You're welcome Lucy..