For 2012, NASA and the Astronomical League are partnering to offer two observing certificates. Completion of the requirements for each certificate will qualify you to download a certificate of completion. Requirements for completion are as follows.
Level 1: Amateur Astronomers who successfully view the transit through a properly filtered telescope (e.g. white light or Ha filters, or one of many projection methods) will receive a certificate of participation in the Sun Earth Day Observing Challenge.
Level 2: Amateur Astronomers will take a picture of the transit and note the time of the observation. Upload the picture so it may be posted on the Sun Earth Day web site and then calculate a value for the AU given one of the techniques described on the site.
You may upload your images of the transit to the NASA Flickr account. There, you will find instructions for upload including details of the necessary metadata to be included with each image.
The largest, single, challenge for astronauts traveling to Mars will be to overcome exposure to solar storms and radiation.