Normally I too would suggest Roland or Korg digital pianos - or the simpler Yamaha Clavinovas. If someone is starting out on piano, personally I think it's quite important that they become accustomed to the weighted action as well as dynamic sensitivity early on. In younger players especially, since some of them may not yet have the physical strength for a proper forte touch, a good teacher will need to assess how much technique they need to know, as well as the means of finding their way around the keyboard. If they're working too hard at pounding away to get the right sort of forte and becoming exhausted, they won't enjoy it as much. Some may think "well isn't that an argument for a non-weighted keyboard?" Possibly, however, feeling the weight underneath their fingers is also important so that the student can assess for themselves how much they're willing to give it.
Whilst I'm not usually a supporter of Casio products, the last time I tried one of their Privia pianos, I was quite surprised at it's playability and thought it would make a good learning instrument. It's not difficult these days to pick up a well priced, 2nd-hand 88-note weighted action digital (any manufacturer) and they can be perfectly good instruments to start off with, and they do of course take up much less space than a real piano if that is an issue.
As for the roll up keyboards - afaic it would be a hearty
NO WAY from me!! I mucked around with one in a store and it was rubbish. Interesting from a gimmicky point of view but for keyboard technique it was crap - you may as well be trying to play a cardboard cutout of the keyboard as all you're doing is hitting a switch, there is no key travel or springing back under your finger. If it has to be one of those, I'd much rather it was several times larger so you could do this with it (at least you'd get fit!)
http://www.youtube.com/watch?v=te4SqP-X8GA&feature=related