The preview takes about a second to see. It would be better if they had something to where it labels it instantly. It will take less time to see what is going on and would use less resources than the previews. Its only an idea, and I thought it was a good one that I liked....
I know what the icons mean to but when you have multiple windows for a application it would be easier to see what is what when it would show you what it is after you hover over it. Then when you choose something then it will go back to the clean tight new taskbar.... cleans the mess...