I was suprised by the number of users whose photobucket accounts are not protected, meaning that I could (if I was so inclined) view every single photo that they had hosted.

If thats what you want thats fine. I have one or two pics in my photobucket that I wouldn't want everyone to be able to view so my account is protected.
If you want to know how to protect your account its really really easy
Log in, go to account options and then in the options under album settings set it to private and use some kind of meaningful password (don't put "password" or something like that or your main account pwd)

Then if someone who is inclined to hack into your photobucket has a go they are a whole heap less likely to be able to....
If you have questions feel free to PM Me.