Context
I designed these icons for the main toolbar of a customizable portal (AFC@work) within MITRE. MITRE works with the Air Force and a majority of its employees are middle-aged users that prefer design that is easy to read and understand. Taking the audience into account, these icons are much larger than the typical style that you would see on a service like Facebook.
Process
For consistency, I designed within the constraint of an icon template that included the star and bubble background shown in the icon's rollover state (which you can roll over and view).
Although the first icon looks like Twister, it was the logo for ENWeb, an internal service at MITRE. Most of the icons represent MITRE services, about half of which have their own logos. As these icons would be used by employees who connect logos to services, I incorporated a service's logo (when applicable) into its design.
If you scan the first row, you will see a difference in the font. This shift happened as the project evolved to include a "create your own" icon, which would use a generic image and whatever name the user gave it. The font started as Myriad Pro (seen in the first three icons), but because user-generated icons would require a web-defined typeface, the font changed to Verdana so that it would look the same in the designed and user-created icons.