Google maps seems pretty cool. Certainly the interface is interesting. Not everything is perfect but dragging the map around is nicer than clicking "scroll left" like most map systems.
On top of that, it has an API letting you easily integrate it into your website which is a great idea. Unfortunately though, in acutally use here in Japan it sucks.
For example, lets say you wanted to go to a some restaurant, you type in the address in Google and this comes up.
Can you even tell there is a subway station there? Check out the larger image and notice there is almost no information.
Now check out Yahoo maps for Japan.
Hey, there's a station here. Not only that, if you are familar with the color
codes of the various subway lines you can see the blue, green and purple lines
go to this station. Blue is the Toei line, Green is the Shinjuku line, Purple
is the Honzomon line. Even if you didn't know the names of the lines you could
go by color and just check a subway map. With the Google one you wouldn't even
know a subway exists let alone what lines.
Yahoo offers even more though. On the left side of the screen is a bunch of
info. 
Including a key for the icons, a list of all the closest stations to the spot
marked on the map and how far away they are by walking. In this case Kudanshita
station (1min), Jimbocho station (8mins), Takebashi station (10mins),
Suidobashi station (11) minutes, Iidabashi station (11 minutes). So, for
example if you know getting to one of the 3 lines mentioned before is out of
your way but you know the line nearest to you goes through one of these closer
station you now know the easiest way for you to get where you want to go.
Below each of those stations is a link to show you how to get there. Click the "make this the destnation 到着 link" and then type in where you are and Yahoo will tell you what trains to take to get there
I even get a weather report for that area.
Why did I post this? Because I've been seeing sites starting to use Google and it's making their sites HARDER to use. For example the Bento.com, a great site for restaurant info, recently switched to google. Let's say I want to go to Den Den Den. I check the map and because it missing any reference to subways there's no way a foreigner would be able to figure it out. Many Japanese could not even figure it out if they were not from Tokyo. Checking out the same map on Yahoo I can see the immediately the Ginza line, the Marunouchi line, the Chiyoda line and several others. I get a list of 5 stations all within 9 minutes of walking there. Even if I didn't know the area I could look at a map of the subway system, find the place that the green, gold and red lines cross and figure out where to go.
I'm not promoting yahoo either. Although they are better than google in this case so it just about every other Japanese map site. Mapion for instance shows the subway lines and as links to stations, bus stops, parking lots and other things.
My impression is, programmers and other web nerds are deciding to use google because they consider it cool, because the UI appears slick and because there is a nice API. Unfortunately they are making it harder for their customers to find the very places they are trying to help them find.