I assume you mean when you say post their logbooks for free , that you mean people will be able to enter their logbook details online for their own use and not for others to see???? There is already a site for this which is jar-ppl.com .If you inted to do a diary of your training this has been done many times , see private flying sections there is a curent thread entiltled "not another ppl diary " This is also a more suitable place for you to post unles you are commercially bound , you will find more PPL related stuff there