I found this video on Conan O'Brien chatting with four other writers from the Simpsons. They talk about the history, dealing with FOX, dealing with guest stars, and a lot of things that happened behind the scenes.
It's long, very long, 81 minutes, but interesting to fans.
One tidbit was the show with Michael Jackson guesting. They sent him a rough draft and asked if he would do a show. He sent it back with a couple very funny jokes penciled in, and said he'd love to, So they sent him the final script, and he showed up knowing his lines and very cooperative... unlike some guests.
So they are taping away and it comes time for him to sing the first of his songs, he stops dead, and motions to one of his entourage to come in the booth. Everybody's looking at each other like WTF, and this little white dude comes in the booth and starts singing Jacko's song.
Turns out the dude was the Lennon Sister's little brother, and he sang it perfectly, just like Jacko. There was some kind of contractual problem with Jacko singing on the show. I didn't know they had singing voice doubles, it makes me think of Milli Vanilli, but of course Jacko could sing.
Oh, they all agreed Johnny Carson was probably the finest human being in show business.
There's much more.