I can hear up to about 20kHz, I don't think you're missing that much, but dog's can hear up to about 60kHz, so I guess we're all missing something! If anyone is interested in testing their hearing, you can use this free online tone generator:
[a href="http://www.audionotch.com/app/tune" rel="nofollow"]http://www.audionotch.com/app/tune[/a]
Full disclosure: I wrote the tone generator, along with the rest of the site to help people with tinnitus create notched music therapy.