Viscosity can be uninstalled by simply quitting Viscosity and then dragging the Viscosity application to the Trash. In most cases the Viscosity application can be found at:

/Applications/Viscosity.app

If you also wish to remove Viscosity's Preferences file, drag the following file to the Trash:

Your Home Folder/Library/Preferences/com.viscosityvpn.Viscosity.plist

If you also wish to remove Viscosity's connection data for your connections, drag the following folder to the Trash:

Your Home Folder/Library/Application Support/Viscosity

A common mistake when attempting to uninstall Viscosity is to look in the wrong Library folder. Mac OS X contains two Library folders: a global one on your system drive and one in your Home folder. When accessing the above paths please make sure you are going through the Library folder in your Home folder, rather than the global Library folder.

Mac OS 10.7 (Lion) users: The Library folder in your Home Folder is hidden under Lion. To get to it you'll need to open the "Go" menu in the Finder, and select "Go to folder...". Enter "~/Library" (no quotes) and click the Go button. Your Library folder will open.