There is a school of thought that is rife amongst the more timid of the lesser spotted Project Manager, and that is that if you ignore something for long enough, it will go away.
While this may be true for such things as his acne and his girlfriend, it is generally never true about software projects. If you ignore a small thing long enough, it will become a big thing and when it becomes a big thing, you are more likely to feel the pain.
Of course, if you know what you’re doing you will be aware of even the small things on your project and will make a conscious decision on whether you should do something about it sharpish or you can safely let it ride for a while.
What you do about it will, of course, depend on the issue and your own personal style but be sure you do something and don’t just defer the decision till tomorrow. Tomorrow will have enough challenges of its own.