The Spiderman/Cat in the Hat breakfast is great, Spidey talks and interacts with everyone and the Cat in the Hat characters are fun also, the food is good normal breakfast stuff. We went at 10:15 am on a thursday and most of the crowd was gone and Spidey talked to use for a good amount of time.
Depending on the season. If it will be busy yes book in advance. I imagine if it is quiet you should be able to walk in. Its located inside IOA at Confisco's.
It isn't under Guest services but "Hot Deals and News"
From the link posted above:
"Swing in for a Character Breakfast at Islands Of Adventure!
Have breakfast at Islands of Adventure with Spider-Man® and the Cat in the Hat Wednesdays through Sundays from park opening to 10:30 a.m. at Confisco Grille.
After meeting the Marvel Super Heroes and Dr. Seuss Characters, experience high-flying excitement on the The Amazing Adventures of Spider-Man ride, with your paid admission to Islands of Adventure.
The breakfast is $15.95 for Adults and $9.95 for children, plus tax and gratuity. Call 407-224-4012 for reservations."
I posted my review of this great character breakfast on another thread, but I go whenever I'm in Orlando. The food's pretty good, the character interaction is the best I've ever seen at any character breakfast, and if you go on a slow day, the characters will actually sit down with you and help feed your kids!