Most of the time you would have no idea you are floating - it's very stable. My mum gets terrible sea sickness (the trip to Macau, for example, was very unpleasant for her and I think those cats are great) but she had no problems whatsoever when she came to stay. Every so often, another boat passes by outside and you get the wash and move a little - just enough to notice but not enough to make anything move/fall over (even balanced items like my nearly empty shampoo standing upside down in the bathroom).
When typhoons come through it gets abit more exciting. We add ropes and pull off from the jetty abit - yes, the boat moves then but we have sat through several 8's and a 9 without damage (but difficult to sleep!).
And oh yes, sure is a conversation starter!