Mike,
My biggest grumble by far is that the session time-out is too short and breaks the flow of the planning process. Anybody using the site for planning will be logged on for more than the 10-15mins. It is irritating to to have to log on again after pondering a different route or whatever.
My other grumble, albeit minor, is that I need to use Internet Explorer. My fave - Netscape 7 - seems to be incompatible.
Other than that I find the whole thing to be of sufficient performance, accurate and pretty easy to use, esp the Narrow Route.
Cheers,
HWD.