> Since it's not a standard, it isn't terribly future proof. It's not supposed to work under the application/xhtml+xml MIME type that XHTML documents are supposed to be served under. (Firefox 1.5 changed this by allowing it for some reason)
># innerHTML is a string. The DOM is not a string, it's a hierarchal object structure. Shoving a string into an object is impure and similar to wrapping a spaghetti noodle around an orange and calling it lunch.
# It makes for some nearly illegible code in a lot of instances, with escaped quotes and plus signs all over the place appending data to the string, which in my opinion makes it difficult to maintain.