Biking Bis blog has a story about efforts to get Google to add bike trails and safe bike routing to Google Maps.
Edit: The previous link was incorrect. Click here for the correct link.
This would be great addition to Google Maps in exactly the same way that Google Transit was(see my previous post here: http://tomorrowmorningsweather.blogspot.com/2008/02/google-transit-helps-with-finding.html#links).
As far as I can tell, it would be as simple as adding the bike only path ways and tagging them as such (so that they don't turn up in driving directions). The next part would be a little harder which would be giving suggestions on the safest bike routes (based on roads with bike lanes, posted bike routes, etc.). Seems easy enough to me, but then I'm not really smart enough to be working at Google, so what do I know?
Anyway, head on over to Biking Bis for a link to the petition so you can sign it.