More then 90% of my clients are online and i have been doing this for about 3 months now, although i dont have website fully complete yet i do have the basics for all my clients.
A place where they can keep track of there diet, workouts and journals, i currently use itrainharder.com for that as it implies the KISS (keep it simple stupid) principal
I have a private forum within my free forum for clients only, this is where one on ones are given and also other clients that i have can support other clients i have so its a win-win situation for all paid clients hehehe.
I have created a microsoft health questionnaire that can be filled out offline then emailed to me or directly pasted into email program.
The best comments i have had from clients is online personal training is better then offline because there is no meetings or commute time you can do it in a gym or at home i like that!
Hope this helps i can email you my questionnaire and other goodies if you want.