I'm a bit surprised at the vehemence of the comments against the cycler track.
I'm going to continue to disagree with the general theme of the comments though. I have actually never had problems with the Vassar paths I find them a pleasure to ride on, and go out of my way sometimes to ride them. I'm not going terribly fast, and I've never had a pedestrian conflict that wasn't simply resolved with a ding of the bell. They've also been pretty well plowed when I've been over there in the winter. I understand that turning traffic is a problem, but to my mind it's just as much a problem with a bike lane as it is a cycle track, and the cycle track even seems like it would be better, since it's grade separated, and they're going to have to go up and over it, which would slow them down much as a speed bump would.
I understand the normal arguments about the danger of "sidewalk" cycling, but this to me seems very different- it's just an extension of the street, not separated by trees or yard or parked cars like a normal sidewalk. Therefore, I think that the cars are going to be just as aware of you as they would be if you were on the same level as they are.
I know that Cambridge owns a special narrow snow plow that they use on facilities at Fresh pond, and I see no reason why not to expect them to plow this facility as well as they plow that- which in my experience is pretty well. I suspect it would be much better than a bicycle lane, because it won't get mounded full of snow at the edge of the road. It's our job as cyclists to help remind them of its importance if they forget. I bet we can train them pretty quick to clear it in a timely manner.
No, a cycle track will not allow you to stop thinking about cars. Yes, you will still need to pay attention at intersections and turning points. But you won't have to worry about people carelessly drifting into you as they talk on the phone, or try to squeeze around a turning car. And you won't feel like your choices are to either allow people to pass in the lane perilously closely, or to take the lane and go as fast as you possibly can so that people don't get pissed off at you taking up so much of "their" road.
I can do the latter, but there sure are days when I don't want to, and wish I didn't have to. For all the people who can't physically or emotionally do the latter, I think that the cycle track is a good option.
If you really feel that it slows you down too much and miss the excitement of playing in traffic, Cambridge has no bike lane use requirement, so if you're young and strong of leg and mind, I'm sure you can continue to practice vehicular cycling in the traffic lane.