such mapping is legal in the US... btw, you dont have to change the SSID just turn its 'announcement' off (the router should have this option... if it doesnt... look into a firmware update... still not? get a router that isnt owned by your isp).... the wireless devices that already know about your router will still connect as usual the only difference being that if you want to add a new device you need to type the SSID manually instead of 'searching for available networks' for it....
oh and... be sure to change that default password... k?
(1) Why do Google need this information?
(2) What do they intend to do with it?
1 & 2 ; google maps --- example use; wifi access points 'foobar1' 'l33tman' and 'starbuck9' are in proximity to the a restaruant you are looking for and your portable device does not have a GPS reciver... (netbook as example of such a device)....
nother example use --- you have a cell but the data rates arent so great where you are.... the map can then be used with a GPS phone to find an open/free access point to send in that business report or..... whatever else you may want to do with a connection faster than what most cells give...
that was the idea anyway... but as they say... the best-laid plans of mice and men oft go astray...
as for their 'wisnort' gathered data... um... their bad? (hell of a 'my bad' situation tho...)