It does remain the same, however your connection will have a max download speed and max upload speed. What if your neighbor uses all or most of it and when you try to download something you don't get with the speed you should.... how'd you feel when you come to know that it was because of your neighbor using your net connection?
I live in a neighborhood where everybody has their own connection . There are is no free loaders in this neighborhood. Actualy it is true for all of America. If a couple of people share my wireless I do not see any load issue. In my own house we have three laptops and one pc in use and we never saw any speed related issues.
I am talking about a case in which someones network is down and they use neighbor's wireless connection which is open.