I don't think that we have the power or means to make a day "unforgettable" in a good way, We do however have the potential to ruin the final part of it, ( amp blew with no backup, played thrash metal all night, etc etc. ) The best we can hope for is to be a major part in making the whole day an enjoyable experience for as many people as possible.
So, to answer your question, Darren: No, I don't believe the hype you've quoted. It is just that, hype.
No. We are more. ( Brace yourself Ian, you've given me the chance to re-open a can of worms particularly close to me heart. ) We are Entertainers.
Get it wrong, and half the guests go home in the first hour. Get it right, and they stay to the bitter end, and give you a round of applause. If the bar staff are slow serving a pint, it's not as much of an issue as a crap disco.
After due consideration of all possible replies, the humorous opportunities, and the potential for swift and severe retribution, I feel I can best answer Shaun thus: