The Google Maps API blog talks about adding driving directions to their API. This is something that I am excited about adding to Where's Tim. I've had directions to me on my real time GPS site for a while (see the post here), but I've always just shelled out a url to maps.google.com. Now I can retain the users of that feature on my site and not have to send them away (hoping that they will come back).
This is also big for the mashup "industry" as well. Visually understanding where an object resides is only half the picture. People care about how something impacts them and being able to offer people directions to your object is the other half of the picture. As developers, we get to offer more functionality to our site, and offer this functionality as if we generated it ourselves. I haven't dug in deep enough to know if we can add our own formatting to the directions div. It would be nice to maintain the same look and feel that we already have to our site (even though I haven't added much formatting that deviates from maps.google.com).
If Google really wants to take a bite out of the big boys and their desktop mapping applications, they need to add reverse geocoding and an fast API call that will return driving distance and driving time between two points for route analysis/optimization applications.