[kbuck]

Browsers that do support SNI include:

IE7+ (unless running on Windows XP)

Firefox 2.0 and later

Opera 8.0 and later

Chrome 6 and later (unless running on Windows XP)

Safari 3.0 and later

Android default browser on Android 3.0 and later (this is probably the biggest chunk of users)

Windows Phone 7

So, realistically, you're looking at people who still use Windows XP (unless they're using Firefox) and people with really old Android phones that'll never receive a manufacturer firmware update.