That answers my question - the thumbnail is supposed to be the icon. The icon loads immediately. (In Adobe, when I select a file folder to open a pdf from and the display is set for large icons, it takes a few seconds for the icon to turn into a mini-image of the document). Since I'm on dial-up, I thought maybe my connection was giving up on something. But as there's nothing more than the icon to see, there's no more worries on this issue :)
Thanks again,
Liz