Jeff Atwood posted a very interesting article today detailing the effects of icons, text, and combinations of the two in toolbars. I particularly liked his comparison of using different icon sets for toolbars. The image of Word with all possible toolbars displayed was particularly horrifying, though.
There is something to be said for having both icons and text. I think of Outlook a few years ago versus Outlook today. I believe Outlook 97 defaulted to just displaying icons. It was also one of the most complicated email programs out there. Today, Outlook is my preferred email client, and it has a nice combination of displaying ToolStrip items with icons and text both. The text tells us exactly what it does, but the icons do have meaning. I keep thinking back to all of the comments to posts on the IEBlog. There was a lot of positive response to the standardization of the RSS icon. There have been a lot of negative responses to some of the changes to the other IE icons, though, in particularly the combination of refresh and stop that they had prior to the Beta 2 Preview. (that might have more to do with having one button do multiple things, though).
Anyway, as I said, an interesting post, so check it out!