I just joined stackoverflow.com and have found that, if I wanted to use the other Stack Exchange sites like programmers, meta, photography, etc., for each one I have to create a new account. Why can't I have one account for all the sites belonging to Stack Exchange. I understand that badges from one site are not applicable to other sites, but how about generic badges or military-like decorations?
There isn't one account. Your accounts are linked instead.
Log in with the same OpenID, email, etc you used on stackoverflow, on any other stackexchange website and it will ask if you want to link up your related accounts.
Then, if you goto your profile you'll see : Stats|Prefs|Accounts With all your accounts on the stackexchange network.
Most users here have accounts linked up. You can also have your bio copied across all sites.