Hmm.... Some suggestions don't really appeal to me because its no point blogging about something you are not able to see or measure change over the period of 30 days. Either Steve makes a change in his life from day 1 and documents the changes over 30 days (how would he do this in the sex / abstinence trials? not very feasible)
Or he starts using 30 days as the timespan of a project. Instead of documenting the changes in his body, I would be more interested in a project management overview over 30 days of how he aligns himself to accomplish something - like mastering a new technology, or any other complex project.
Passing an extremely difficult exam (in a topic Steve is totally unfamiliar with) in 30 days... to winning a dance competition that occurs in 30 days {I'm drawing inspiration from MTV's "made" here
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Also, I'm not exactly aware of how much you are up for to showing yourself to blog viewers, but maybe you should also consider video-blogging? It would definitely enhance the 30 day trial in my opinion...