Yeah...to be honest I got a lil freaked out when I got my first reminder email. I was like _So what, what's it to ya? So what if I havent been around lately, been busy._
lol

The other option would be to track total members and then ACTIVE members but like you said above who's to say what the definition of ACTIVE is...within 1 week, 1 month, 2 months, etc.