It is good to have goals, and the 30 hubs in 30 days challenge can help define those goals for you. However, it is important to produce quality hubs. If you have the time, and are able to, write a quality hub a day, then the challenge is a good one for you.
Especially if you announce it, and others support you in your efforts.
If you don't have that kind of time, or can't write a quality hub a day, then it isn't a good one for you. Remember that 30 hubs in 30 days requires one quality hub every single day, even weekends, and even when something else comes up, unless you can write more than one hub a day to catch up.
If you find that you have run behind, and rush out some hubs just to meet the challenge, you may have wasted your time, at least on those days.
I have taken the 30/30 and the 100/30 challenge. I was able to meet the 30/30 with no problems, so I would recommend it. It provides a good structure and keeps you going.
I also recommend that you choose a number that works well with your schedule and abilities. Right now, I have created my own goals and am working to meet them. On the days when I don't meet the goal, I forgive myself and try again the next day.