When faced with a drinking evening, you can just drift along hoping you'll run into a friend, or make annoyingly formal plans that'll make you feel like a leper when everyone ignores them. For casually effective planning, try Barbound
Launched in SF, BB's a GMap-enabled repository for users' drinking agendas that'll allow friends to see what's on tap for the night, and allow you to keep your cellie pocketed, where it'll fulfill its primary purpose -- making your penis look bigger, and more sharply- cornered.
Simply build a barhopping itinerary and it'll be posted on your profile for all to see; or, when grindingly alone at the Endup, for all to have not seen.
If you don't have your own agenda, troll the bar listings to see who's hitting what, or search through friends'/strangers' profiles and plan your evening around them -- an option that makes stalking so easy, it ought to be a crime
Being in beta, BB does have some issues: users can only log in thru Gmail accounts, and your itinerary must be selected from a preset list of bars.
If your destination's not listed, you can include custom details on the Facebook-Wall-style "Cocktail Napkin" -- though this must be proactively sent to friends, who'll ignore your entreaties even as your finger falls off on the keyboard.