I agree with the majority on this issue.
While I understand that sometimes, things do come up, those who make it habitual get on my "never make plans with that person" list.
And cancellations are one thing. No-shows or standing someone up (without a real emergency) is unforgiveable.
If you have to cancel, then call (or email) and cancel. Simply failing to show up is not an option, and immediately puts someone on my "no further contact" list. Well, almost. They get one chance to explain; if it was not an emergency, I'll tell them I think they are shitty, and request no further contact. If they were in a serious accident, had a medical emergency, or a death in the family, that's understandable.