On the ride back from the english scottish ball I read steve krug's don't make me think, which is an excellent book on web usability. With his suggestions in mind, I redid the top part of the mbtaplot interface, changing from:

to

Specific changes:

• added site id "MBTA Plot" at the top, so people know what site they're on
• added tagline "less waiting out in the cold" below the site id so people get an idea of why this site might be helpful to them
• explained address box by putting "Type an Address Here" in the search box, with the text initially grey and disappearing when you click on it for the first time. Otherwise it's not clear what sort of things you can put in the box or why you would put anything there at all.
• capitalized 'go' button because that's apparently more standard
• hid 'remove route' until there's a route to remove. It's confusing to first time visitors to have more options, and until you've added at least one route it's a useless dropdown.
• renamed 'intro' to 'help and introduction'
• removed 'permalink' because it's no longer needed (as of a couple weeks ago, the url is constantly updated to reflect your changes
• remove checkboxes that confuse navigation and are only useful to advanced users
• moved controls to one line to make it clearer what order you do things in

Other suggestions?

Update 2011-02-15: people suggested several other things, which I've fixed:

• renamed 'add route' to 'see routes near here'
• change 'see routes near here' to 'more routes near here' once you've added at least one
• renamed 'remove route' to 'hide route'
• capitalized 'help and introduction' to make it more prominent for people who need it