For example, are there any general trends wrt assistant professors as compared to tenured professors? I'm sure that the variation between types of professors is lower than the variation between professors of the same type - but there could possibly be special cases where the type of professor who gives out recommendations may matter.
And what of the departmental reputation? Sakky said in the old "MIT is a complete joke" thread that a stellar student could go into a state school and do exceptionally well in that state school. But then - there's the issue of the reputation of those who can issue out recommendations. And not all highly motivated students will necessarily get exceptionally well GPAs in state schools - and these students will need research to offset lower GPAs.
And in the case of a famous but jaded professor vs. an enthusiastic but non-tenured assistant professor - would the recommendation from the former type of professor matter more? (even if the latter type of professor may be more enthusiastic in helping the student out?)
And then - how can I tell which people are the most reliable in giving out recs, and the ones who aren't so reliable?