For the chronically absent:
"A man like him is hard to find." "It seemed his career was just taking off."

For the office drunk:
"I feel his real talent is wasted here." "We generally found him loaded with work to do."

For an employee with no ambition:
"He could not care less about the number of hours he had to put in."
"You would indeed be fortunate to get this person to work for you."
"He consistently achieves the standards he sets for himself."

For an employee who is so unproductive that the job is better left unfilled:
"I can assure you that no person would be better for the job."

For an employee who is not worth further consideration as a job candidate:
"I would urge you to waste no time in making this candidate an offer of employment."
"All in all, I cannot say enough good things about this candidate or recommend him too highly."