This is something I dislike, personally, but it appears here for the sake of completeness. I have a number of reasons for disliking it: firstly, I like to see the progress when I am downloading a page, and this interferes with that; I also like to see where a link is going to take me by placing the cursor over the link without clicking; I can't do that with a scrolling message in the way. Some early JavaScripts of this type can cause the browser to lock up or crash; and lastly, it's boring after the first repetition.

Hey, it's my status bar, OK?