I did this last week in preparation for racing on Wednesday: haul up Mass Ave to Lexington Center and back. Its nothing long and I see its purpose as making sure my legs are warmed up for the next day; from Cambridge Bike its just a hair shy of 10 miles each way with a nice park in Lexington to catch your breath at. If enough people are interested, we could make this a weekly thing, maybe tack some extra miles onto it/change the route weekly.
I'll be out of town tomorrow morning and a good chunk of the afternoon, but should be back in time to do this. Meet at 7pm at CB. If I'm not there, head out without me.