http://citytours.googlelabs.com/?reset=true

It looks like you put in a place, and it recommends things for you to do in that city, like, actually plans out your day. I used the recommended search for Dublin, Ireland [http://citytours.googlelabs.com/search?city=Dublin,%20Ireland] because I've spent a lot of time there and let me tell you – this is impressive. It gives you a 3 day tour to start, but you can specify dates and everything. It displays a map on the right, and your tour on the left. Here is an excerpt from Dublin's one:

*walk about 35 minutes

Guinness Storehouse
09:35, for 75 minutes
  
   *walk about 10 minutes

Collins Barracks
11:00, for 75 minutes
  
*walk about 45 minutes

Chester Beatty Library
13:00, for 60 minutes
  
*walk about 1 minutes

Dublin Castle
14:01, for 45 minutes.

~~~~~~

Those are very good lengths for the time walking between and to spend at each place.

http://img151.yfrog.com/img151/2971/vwo.png

How does it know you have to spent 45 minutes to visit Dublin Castle?

I dunno, but it's about right...