Not really secrets, but cool things some people don't know - you can arrange for a wake-up call to your room, and it might be from Mickey/Goofy/Donald etc... (or at least was last time I went!)
If one of you has a birthday, let your Disney hotel concierge know and you don't just get a button, but they can arrange (if you ask nicely) for your favourite character to send a birthday card to your room on that day - I got my husband a Sorceror Mickey Birthday card, signed by Mickey and a balloon, all for free - Disney is so lovely! (I offered to pay and was told it was free!)
The camel in Magic Kingdom by Aladdin's carpet ride that spits water every few minutes, and Stitch above the entrance to the
Disney Store in Downtown Marketplace also spits water every so often. I enjoy watching kids unable to understand how they just got wet!

So cute!
Miranda