What happens when i factory reset my android phone?

Your sd card wont get deleted, it only deletes all the apps on the phone, and yes you will be able to log back in to your apps, so if you have all your apps backed up, just reset the phone, download mybackup from the market, and all ur apps will be there since they are all backed up to the sd, just reiinstall them, but any saved data on the apps wont be there anymore, so if you have like angry birds you will have to start all over again.