I've seen people zooming by on that path on Fresh Pond. I'm not a fan of bike paths, but if I lived in an area like Arlington or Cambridge, I would most certainly use one to commute. My son's car died yesterday and while he is in the process of getting a new one, his boss gave him a bike to use. I am scared to death; he lives in JP and works in Cleveland Circle. He is not a cyclist, although my husband did give him a lesson on the rules of the road for riding a couple of years ago when he commuted to a summer job during college. I reminded him to buy a helmet.
I did commute yesterday. My times are getting faster, even though it was so hot and humid yesterday. On my ride in, I had a shrug over my sleeveless jersey and a wind jacket. I had to stop half way and take the shrug off. It was like I was in a sauna. My husband did come and meet me in the afternoon (it sent some of my students off the deep edge to see a man in spandex). I lead him back for the first half of the ride, but I got tired of pulling and let him lead before we started going up Pope Rd. in Acton.
AM commute: 14.3 miles, average 15.01 (it's a false flat the whole way, with one climb)
PM commute: 14.7 miles, average 15.8 , small downhills, with 2 big climbs at the end