I always thought Century Gothic was safe to use, that its installed pretty much on every machine.
However, it appears that my new installation of Windows 7 does not have that font!
Is Century Gothic safe to use? Is there something wrong with my installation?
according to this no, less than 88% of machines had it installed...
Whether or not a font is "web safe" is going to depend on your own standards for minimum percentage of people who have access to that font.
According to: http://www.mightymeta.co.uk/web-safe-font-cheat-sheet-v-2-including-google-font-api/ Century Gothic appears on approximately 84% of computers (this number comes from combining data from the survey Tony Crockford posted, as well as one other source).
Being "web safe" is not a yes or no question; there is no font which appears on 100% of internet connected computers. What you should be looking for is fonts with a higher likelyhood of being on most of your viewers' computers (a higher percentage). Since no single font scores a "100" this is why font stacks were created, allowing you to list two or more similar fonts as "fall back" fonts if the previous is unavailable.
Your best bet is a font stack of (at least) Helvetica and Arial, which numbers show should provide you with approximately 99% coverage.