This was an interesting video on the way to create separated bicycle lanes in an urban city. For commuting I would like to see this through a city, but this is a commuting solution and should not be sold as a recreation solution for families in my opinion.
A solution that makes it easier on cars to co-exist is cool with me. Physical barriers are even better idea. Making a city more bike friendly can be done with better design, but we need to remember the solution for one area or one street may not be viable in other areas. Therefore, having more options is best.
I could see Seattle finally closing 3rd Avenue through dowtown for cyclists. The next step is insuring that you have traffic avenues to downtown that are safe for cyclists as well.