Yeah, a lot of us are geeks.
Anyway, yes, formatting your HD will wipe out the cookies you have in your browser but, of course, will not affect the data in the web server at Susans.
You will have to log in again when you get everything back up and running, but after that you'll be fine.
BTW: Why are you wanting to reformat? Usually there is a pretty serious reason, like hardware failure or virus infestation. Just curious.
-Sandy