Yes its quite common now. Working in my high schools theater which was the largest in the town we'd get these types of requests so I imagine in they would be even more common for something that mattered
Sometimes these riders serve a purpose (Van Halen's case), sometimes they are indeed a caprice, or a joke. If I recall correctly it was Pearl Jam, who once demanded their M&M's to be segregated into jars, and each jar could only contain one color of a candy. There were photos floating around the net with the band members laughing and posing with that jars and the guy who felt into the trap. Oh, life of a rock star ;)