They recommend 20 minutes a day i hope there isnt cos im just about to go back to work after a 2 month break and im an outdoor activity instructor at a scools residential site so far bit of exercise involved and im planning on doing ws while im there!
It depends on what you are used to - if you are used to swimming Swim! If you are not used to anything just try to walk a bit more, ten mins to start then increase it gradually.
I swim and did on Exante TS but I was used to swimming, as ever don't do anything that does not feel good or feels a strain. Just build it up very gradually. There is no doubt any exercise helps now and later when you are trying to maintain.
I use a pedometer but agree i am just a bit obsessed. The only way to eat a bit more later is to get into the exercise thing.