Starting the 90 day blog challenge on Friday the 26th of April 2013 would put it at day 73 of the Challenge today (!). It has been a fun and interesting (for me at least) little game we've been playing.
Having various challenges on the boil makes life more interesting, I would say.. My wife and I started doing challenges a fair while ago. I don't remember the specific details of the first one, or how it started; but one of our earlier challenges involved each of us picking an unconscious habit the other one did a lot - then seeing if we could catch the other one out. First person to be picked up doing the habit 10 times lost, and had to do a set 'task' decided by the other person at the beginning of the challenge.
My first unconscious habit (picked by my lovely wife) was saying the word 'epic' too much. I lost this challenge so quickly we created another round of the challenge where I had to watch my use (abuse) of the word 'epic' again.. I lost that one too, but not as quickly or by as much! My use of this word is now down to bordeline normal levels again, but I still laugh when I see the word in a business name or ad.
The challenges are a fun (as long as they are kept friendly) way to work on breaking habits of various sorts. Having someone to keep you honest in the challenge makes adherence better than if you were left to your own devices... having some type of reward worth something for the winner is also another motivating factor worth considering.