having worked over 500 weddings in my job as a banquet manager at a large country club, i can say i've seen more photographers use some type of diffuser on their flash heads.. be it a gary phong light sphere (which i see more than anything else) to stofens to bounce cards.
and having talked to so many of the photographers while they are at work i can honestly say the only place i see diffusers not recommended so heavily is on the internet.
your best bet is to buy the couple of diffusers you want to try, and use them, if you dont like them sell them, that way you know for yourself if its for you or not. i just picked up a gary phong here in the forums for $25 shipped.. beats the $60 new for it thats for sure.. and i can already tell i like it alot.
i look at it like i look at the gun i carry.. i'd rather have it and not need it, than need it and not have it.
Canon 40D|Tamron 17-50mm |430EXII| Next Purchase: 70-200 F4L in the future...