A current post references Democratic family members voting straight ticket. As people head out for early voting, it's a good opportunity to remind people that they may not want to do that.
There may be some variability to voting machines. But on machines of the type I used yesterday, voting a straight ticket means you will not "see" the non partisan candidates. (Not sure if it also excludes bond issues, referenda, etc).
There is a great video by the cast of West Wing on exactly this issue here:
http://www.mccormackforjustice.com/
There is another reason to avoid straight ticket voting - if you live in a very red state, as I do, there may be many races without a Democratic candidate. Voting each race individually means you have a chance to enter a "protest vote" for the Green or Libertarian candidate. I always vote Green, since I believe there are some odious Libertarians. But either choice serves.
(random question - how come the Greens and Libertarians can find warm bodies to run in every race, even though they never get elected, and Democrats can't?)