I find Bing maps to be sluggish as well. I haven't seen the black squares but I do like the birds-eye view which gives me a good feel for where things are better than a satelite picture.
I have noticed that when I first open Bing Maps I have to wait until it is done downloading/rendering before I can even put in the address I am searching for because when it finishes rendering the page it clears out the search text box.
Google, meanwhile, once I can see the text box I can put the address in, hit Enter and it will search that address once it can get to it.
Sometimes Google Maps is slow, but usually it is snappier than Bing in my experiences.