The keyboard clicks annoyed the crap out of me on my very first iPhone. I've had them off for the past 4 1/2 years. Actually, my phone is in vibrate mode probably 80% of the time anyway. I always seem to be in places where alerts/ringtones of any kind would be rude or obnoxious. At home is probably the only place I keep my phone sound on, and even then if I start a text conversation with someone, I'll turn it on vibrate because I get tired of hearing the sounds constantly.
As for the people who need the clicks for feedback, just try it without sometime. I promise you'll still hit the keys. It's not making your a better typer just because you can hear it.