Well, now I have graphical evidence of why my mobile phone doesn't work when I'm at home. I just found T-Mobile's Personal Coverage Check site that maps out their network signal strengths over real maps, and there's an ugly gray blob right over my neighborhood. Bummer... but nothing I didn't already know.
Somehow I've always thought that data at this level was one of those things that all customers wanted but no operators wanted to share. I'm glad to see that change. Of course, if you give enough geo-hackers mobile phones, the data will surface eventually, but it's nice that T-Mobile is actually being honest and showing the strengths and weaknesses of their network.