What is a dangling modifier? Should I be concerned about it? 

A modifier is a word or phrase that modifies or gives more detail about an item in the sentence; usually this item is located in proximate relation to the modifier.  To illustrate it better, here is an example:

As an English teacher, I have worked in five countries and two continents.

    (The English teacher is the same person as "I." The initial phrase is the modifier of the following pronoun.)

A dangling modifier is misplaced, as in the following:

As an English teacher, the rules of grammar become more and more confusing.

    (the rules of grammar are not the same as English teacher...  the sentence is problematic to understand and detangle.)

Yes, be concerned! It is a common problem in complicated texts and can be confusing to your reader. At any rate, the occurance of dangling modifiers makes writing teachers cringe!

Which resources did you use to find the solution? Were the resources useful?