I don't believe that not responding will affect the AI's mood. Some AIs just need to hear from you fairly often to stay happy (they're like women--communication is a positive, and there's a natural decrease in happiness over time). Some AIs don't want to hear from you, and may even become angry at a gift/tribute offer, but may naturally become happier over time. Then there's those lovable, adorable little fuzz balls that just plain hate everyone all the time, no matter what you do.
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The Unpronounceable Krsqk
"Well, sir, at the moment my left processor doesn't know what my right is doing." -
Freefall