CTK501

One of the more experienced members here may be able to answer this better, but i'll give it a go for you.
Web Safe Fonts used to be a much bigger problem than it is now. In previous years, the use of Web Safe Fonts ensured you were using a font that was guaranteed to be compatible in all browsers etc. It is still common practice to use a family of fonts to fall back on like so {font-family:"Times New Roman", Times, serif} however the use of Google Web Fonts ensures compatibility across modern browsers, without requiring the user to have the font previously installed on their system.
 
Google Web Fonts currently supports
 
Google Chrome: version 4.249.4+ Mozilla Firefox: version: 3.5+ Apple Safari: version 3.1+ Opera: version 10.5+ Microsoft Internet Explorer: version 6+ Android 2.2+ and iOS 4.2+ That should have you fairly well covered, but it's always good practice to have a fall back font like i previously said.
The only things that should still be considered is the fact that the Web Font Still has to download to be displayed, this happens automatically and is then cached in the browser. Many of your users may already have your font cached, as Google Web Fonts is quite popular now, however if the user does not have it on first visit they may experience a flash of un-styled text, until the font downloads and applies.
 
I hope that has answered your question and i look forward to hearing and responses from the more experienced users on here. Good Luck