streamline sign in cue text and interface+discussion

I know there was some good editing of the cue text, but it didn't address what was described in +issue here. I took the opportunity now to update the existing example and flesh out the other places i could think of where the proposed change would make sense.

Some nice examples/exploration for whenever we're changing things anyway: http://blog.leahculver.com/2009/11/log-in-or-sign-up.html

  --John Abbe.....Mon Nov 16 15:24:12 -0800 2009

cool. this should be linked to the signin-related ticket I recently created. will do soon.

  --Ethan McCutchen.....Mon Nov 16 15:30:39 -0800 2009