At long last, it's up! BeerRiot Local will show you the breweries it knows about in whatever city your ask.
If you're a registered user, you can even tell it where you'd like it to show by default. If you don't ask for anywhere specific (that is, you leave the field blank), it takes the liberty of sending you to Boston.
This also means that it's now a good idea to add street addresses to the location field for breweries. Otherwise, breweries in the same city will have overlapping markers on the map. I'll be updating the ones that are already here in the next few days.
One word of warning: the map doesn't work in Internet Explorer 6.This has been fixed as of Aug. 16.
There's more up at the blog, if you're interested.