I already said Do not use the style property on HTML objects and as I was thinking how bad the innerHTML property can be, I considered doing an article on that subject. The problem was that stones were thrown at me after the first “Do not” article. Now I fear that this one may be worst… but I'll stand proud…
VS with innerHTML
NO! In fact, you can do it but for every reasons in the world, don't ever do that. Yeah, I know, Yahoo!TV is doing it but don't fall in that trap.
Ajax should return data to your application. Why? Because you'll never know what you'll have to do with that information. For the moment, maybe you just do a simple display of the data but sooner or later, you'll have to re-use for another section of the page. If you return HTML, you will end up parsing it to extract the data contained in it. I tell you.
By the way, forget about that old XML thingy, try JSON…