I have been recruiting for one of my clients recently and I have to tell you, it still get surprised the odd time by unprofessional responses.
It's important to understand that the person interviewing you is trying to predict future behavior. If you can't comply to requests from the interviewer (within reason) you have to understand that they may be making observations on your ability to work as a team, follow leadership, your writing ability and your responsiveness to potential customers.
This is a real email I received and an example of how not to respond:
Sorry but my copier is not working at all at this time. So I will not be able to get you a copy of my resume. But I can confirm that I can make our appointment for Tuesday am. Could you confirm that you got this email and our meeting is confirmed.
If a candidate can not be resourceful enough to find a printer, how hard will he try with a customer?
The use of highlighting and capital letters is perceived as email yelling or making the statement loud. This is not a tone you want to take with a potential employer.
The grammar and writing style uses the same word twice in a sentence and no one should start a sentence with "But".
Responding to a recruiter should not be taken lightly. How you interact now will influence if you are moved forward in the process.