Some of my cocktailian brethren and I were recently bemoaning the lack of authenticity in some cocktails. Take the Manhattan, for example. Long ago, it was a 50/50 mix of rye whiskey and sweet vermouth, with a couple of dashes of orange bitters. Over time, the cocktail has evolved (or in this case, arguably devolved) into rye whiskey with barely any vermouth, bitters only if you're lucky, and a dose of maraschino cherry syrup. I'll pass on the latter version, thank you very much.
See Also: How to Make the Best Manhattan Cocktail
The situation gets even worse when you get into my specialty, tropical drinks. It seems the modus operandi of many tiki bar menus is to come up with a drink that involves lots of rum and fruit juice, then slap a name from an old tiki bar menu on it. Given the fiercely secretive nature of old-time tiki bartenders, it's not surprising that this is the rule rather than the exception.