I thought it was pretty cool that we had started in Somerville and biked to Rhode Island and back already. :-) cfox and I have biked from the Newburyport CR to Plum Island and back to the CR a couple of times. Dealing with the schedule is a little bit of a pain but it's not that bad, particularly if other people are around and/or you have something to read. The approach people took last time ("stop at the last point where we'll be there before the train") works fine if you're actively following the CR route.