Strange to say, the same thing occurred to me just the other day. I am an 'an hotel' person - though I was thumped on it by a Sales Manager whose wife looked up Fowler which states that it is archaic and isn't really best practice business writing. Well, yah boo sucks to Fowler say I.

Funnilly enough, though, I find the American 'erb jarring, and would probably say 'a herb', not 'an herb'. But 'an historical', not 'a historical'.

It's all custom and practice, that's what I think.