Sorry, I got busy with other things. Shawn, It doesn't seem to be the overflow default but that was an excellent thought. I had 5 tabs open across the top in Firefox tonite and Aero Peek in task bar shows text only of the last two pages I looked at. However, I closed all but one tab(Windows Seven Forums) across the top and Aero Peek in task bar still shows text only. There have been Thumbnails previews there for several days and now it shows text only. What a mystery?! I will keep watching and trying to figure when it toggles from one to another. Yes, it is a blue task bar to left and center and then fades to gray
over in icon notification area to the far right.