Jen
My minds gone blank as to what we paid but we did not have an airport transfer on it. It saved a lot of carry on searching for change as you are on and off the MTR all day. ( and also on and off the Star Ferry). We did get money refunded at the airport. Will ask OH and let you know!

http://www.hong-kong-travel.org/Octopus.asp
We did not get the airport express one. Our transfers were included. However, re your question- the two single journeys are for one person as the cards are non transferable.

We had an octopus card when we were there a few years ago- brilliant things. We didn't have the airport express one though, just the normal one
Well worth having for getting about with though- valid on buses, trams, ferries, trains, MTR, even the Kowloon Circle tour.
Remember to get your deposit back at the airport before you leave- very easy just find the machine at the train station downstairs and put the card back in- out pops the deposit.

Thanks guys, still find it confusing. What do they mean by 2 single journeys?? There and back to the airport? That's a return and do you have to take your single journey within 3 days. Dosen't make any sense to me but will still end up buying one, need to get about somehow

the express journeys have to be taken within 180 days- so I think you will be ok! Personally I preferred not to take the train as I am lazy and wanted to use the hotel shuttle taking right to the hotel You can't both use the card for a transfer from the airport- you would need one each.