There's a nice article on ClearVoice which talks about the importance of good grammar.
The blog writer says that people are mostly divided into three camps when it comes to the topic of grammar:
Purists. This group appreciates the grammar rules. They believe in a set of rules which apply to correct usage of words. They tend to think that poor grammar signals the decline of civilization.
Rebels. This group is more interested in what's trendy than the rules which govern grammar. Grammar is not bound by rules, but can be adapted according to common usage. This group probably sees nothing wrong in using text message writing style for most written activities.
Don't-know-don't-care. This group isn't aware of grammar rules, can't remember them, or flat out does not care. They are the ones who'll scoff or roll their eyes while saying, "Who gives a crap? People still understand what I wanted to say."