For the most part, good should be used to describe a condition or passive state, as in "So, that new Angelina Jolie film is good, eh?", as opposed to well, which should be used in instances such as "My computer is running well", as an activity or state of being being described. In these instances, "good" was an adjective describing the noun, and "well" was an adverb, describing the verb. Thus, the reason why it isn't "My computer is running good", as "is running" is the first two terms in the verb phrase. The adverb completes it.

Unlike When to use "who", and when to use "whom", this simple grammatical mistake may make one appear illiterate or unschooled, etc.