"It has been said..." = tactic to avoid actually citing a source, making a claim of fact, and taking responsibility for the writer's thesis. Also, an instant "F" in any writing class that I teach. Also a frequent, lazy-ass tactic used by the Writing Department in WT literature.
Other rhetorical offenders (and I'm soooo glad that readers of this forum pay attention to such things):
"Throughout history..." (Used to avoid giving specific examples and to lend the air of historical authority to a weak claim.)
"Scientists have found..." (Which scientists? Using which methods? What studies? With what limitations? Published where? Peer reviewed? This is also a very sneaky way to avoid actually backing up a claim of fact.)
Feel free to add more. These are just the worst offenders, in both WT publications and freshman comp papers.