I had mine replaced earlier this year after receiving the code. The only thing that I saw change after it failed was my mpg dropped a few...like 5 or 6. :P After replacing the failed one everything returned to normal.
Maybe Bill or Winfred could chime in but I think replacing both while you're under there isn't a bad idea. If you have an indy who works on your car he might be able to pull the codes to see which sensor did fail.