I've ordered these a few times, and had wildly varying results - hardly surprising, given the general lack of training among bartenders around these parts, but confusing none the less!
So now I'm curious: what should a Manhattan be composed of?
A traditional Manhattan is two shots of rye or bourbon, one shot of sweet vermouth, a dash of bitters and a cherry, shaken and strained into a martini glass. I prefer on the rocks in a rocks glass, myself.
A perfect Manhattan is similar, but uses a half shot each of sweet and dry vermouth. They tend to be more interesting when paired with a higher quality whiskey.
I'm also a big fan of white whiskey (aka, high quality moonshine) in Manhattans.
Manhattan's were originally made with Rye rather than Bourbon, but times change and the modern trend for the latter means that Rye often isn't the first choice. Cocktail supremo, David Wondrich, notes that a decent proof Bourbon will work just as well as Rye in an Manhattan.