I have been doing distance learning for about 7 months now and will sit the first subjects in February, having completed the first module. My points are as follows, in no particular order:
1) None of what you have to learn is that hard, what is difficult is the volume and diversity of information you need to know. However it is difficult sometimes being teacher and student.
2) You will be allocated a tutor and make sure you use him/her. I regularly e-mail mine (two or three times a week) with questions and sometimes just stuff in general about aviation - after all these guys are experts and you have to get everything you can from them.
3) At the start of the course it seems like you are making very little progress, as the first subjects are generally Principles of Flight and Systems, big books to wade through. But eventually you finish them and then start on little subjects like VFR/IFR communications and Mass and Balance and you start to feel like you are making real progress. It took me about 6 months to do the first 7 subjects, about 3 months of it was on PoF and Systems, did the other 5 subjects in the remaining three months.
4) If you can get hold of other FTO's question banks that is a massive help. I get given everything from cabair by a mate who went through and that has proved a great help.
5) Now I have started to revise for the exams, many things have started to fall into place, in that several of the subjects are interlinked. For example, PoF/Performance/Mass and Balance, Aviation Law and bits of Performance and Systems.
Good luck