How Many Spaces Between Your Sentences?

Some say one, some say two. Should you care? I have been trained to use two (as you can tell from this posting). I used one when I worked at a newspaper, but that was to save space. Based on my research, it sounds like using two spaces is considered outmoded and based on typewriter functionality, not today's computing reality.

http://www.westminster.edu/staff/nak/courses/spaces.htm
http://desktoppub.about.com/cs/typespacing/a/onetwospaces.htm
http://nayyeri.net/blog/double-spaces-between-sentences/