I haven't done it but have read lots of articles by people who did (we mad cyclists and members of CTC). I expect you'll have a great time, would suggest less than 2 hours in the seat/day to keep toddler happy, ideally some of it during his usual nap times.
lljkk - think the longest distance is around 20 miles so we might be on the road slightly longer but good idea re his nap times.
overmydeadbody - we don't cycle on a regular basis although we always try to on holiday and we love it when we get the chance. Never done it with a LO though! He will be in a trailer (behind my DH). Is it quite tricky? Perhaps we are being silly going with LO before even trying him on a bike. He does love the great ourdoors though and he is dead nosey so I think he will like it.