As noted, in many states the DWI/DUI statutes apply to motor vehicles of just about any sort. Other states simply use "driver of a vehicle" which definitely includes us riders in the mix.

Bob Mionske's recentn book, Bicycling and the Law has a good discussion of the BWI issues and how (and where) they work. Some states would indeed rather that when you get on the whiskey, you take your bike or faithful horse rather than the keys to a motor vehicle...