Simos right , inercia has something to do with it. Artificial Gravity is made that way , I think MIR even used it. Not sure on that one though.

They have been planning the exploration and manned landings on Mars for at least a decade. Hell thats why they sent the rover.
The problem they were having before (outside of funding of corse) was it takes 3 years to get there. No one has ever been in space for that long , you figure anouther 3 to get back and you are talking about the very likley possibillity of severe illness or death from those who go.

Now like you said , they are developing beter and faster ways to get there. That should make the project work much better. Hopefully those propoltion systems will be used in the next 20 years.