It DOES NOT MATTER how many pictures you have compared to storage size. We are strictly talking bandwidth here. Even if you had only one photo that was viewed enough times, you would exceed the allowable amount.
Every single time someone views your picture, it is linked to Photobucket. That view uses bandwidth. There is no way to check or monitor bandwidth, deleting pictures doesn't help either.
I've been tampering with IMGUR and GOOGLE trying to decide which I like better. Presently, GOOGLE is kicking my butt. IMGUR seems to be the most similar to Photobucket.
Here's a thread about Photobucket alternatives:
http://www.rokslide.com/forums/general-discussion-forum/69555-photobucket-alternative.html