A lot of people who are looking for a flat, tight midsection may have the tendency to work their abs every day, but that may not be the answer.
The problem with that is this: Your abs are not different from the other major muscles of the body which means you want to give them (like you would your other muscles) time to recuperate. Keeping that in mind, you really shouldn't work your abs (high intensity ab workout) more than three times per week, allowing at least 48 hours rest between training sessions.
Here is the good news: If you're involved in a regular strength training program, you may even want to think about training your abs even less because you're probably working your abs more than you think. The abdominals act as "stabilizer muscles", which means they help support the spine and maintain balance so they are indirectly involved in just about every exercise (even in the slightest way) that you perform. A lot of exercises (such as squats, overhead presses and swimming) require significant contributions from the abs so basically, your abs are being inadvertently worked every time you work out. In fact, many bodybuilders never really only work on their abs, however most body builders have some serious abs.
Fit's Tip: You may say, "but Fit you told me to do your 4 minute ab video everyday!" Yes I did, but that video is not high intensity (say at least 30 minutes of straight ab work), which is what I am talking about here.