With a record number of head coaching vacancies this offseason in the NFL, it was likely that some of the replacement head coaches would be first-timers.
However, so far, almost all of the hired coaches are first-timers:

Detroit Lions - Rod Marinelli
Green Bay Packers - Mike McCarthy
Houston Texans - Gary Kubiak (deal cannot be announced yet)
Kansas City Chiefs - Herman Edwards (look! a previous head coach!)
New Orleans Saints - Sean Payton
Minnesota Vikings - Brad Childress
St. Louis Rams - Scott Linehan
New York Jets - Eric Mangini

What I fear is happening is that clubs are hiring coaches based on the "potential" idea, and they are hiring based on which candidates perform most impressively at interviews.
Both of those approaches have fundamental flaws. As Bill Parcells famously observed, saying somebody "has potential" is merely a polite way of saying that they haven't done anything yet. And, as observed by Larry Bossidy (former CEO of Allied Signal) in his excellent leadership book "Execution - the discipline of Getting Things Done", there are some leaders who interview well and other leaders who do not interview well. As evidence for that phenomenon in the NFL, I would offer the cautionary tale of the Buffalo Bills, who hired Gregg Williams in 2001, largely on the basis of the fact that he was the most impressive interviewee. That hiring clearly did not work out, and Williams is now back as a co-ordinator.
Lost in this frenzy of hiring bright-eyed young co-ordinators was any serious consideration of more experienced guys who have either been head coaches in the past, or who actually have a sustained track record of achievement in the NFL. How the Green Bay Packers ended up hiring Mike McCarthy, whose previous job was to manage an inept San Francisco 49ers offense, over Jim Bates, an experienced co-ordinator with an excellent track record, is a complete mystery to me. Not surprisingly, Bates has now left the club. Elsewhere, other experienced co-ordinators like Al Saunders of Kansas City and Ted Cottrell are also finding it hard to be taken seriously as candidates.
The St. Louis Rams have also offered their head coaching position to offensive co-ordinator Scott Linehan of the Miami Dolphins. One of the candidates, Ron Rivera, apparently did not impress in his interview because his coaching plans were "less detailed" than those proposed by Scott Linehan.
Let's get one thing straight here. A look at the track record of NFL franchises shows that a major factor in sustained success is stability. You do not win in the NFL by turning the club upside down every other season. That being the case, a guy who promises a "new broom" approach may not be the best answer. Not everybody in a club is useless if the club is not winning. Extending that logic further, an interview candidate who presents a detailed action plan would worry me, because that tells me that the candidate has preconceptions about what will work, which is presumptuousness bordering on arrogance. I would be more impressed by a candidate who has a clear philosophy, a track record of success over a longer period, and who promises to be objective in evaluations of the current situation. You can infer from this that if the reports are correct, the Rams' hiring criteria are missing one or two fundamental issues.

It is my opinion that a number of these clubs will be disappointed in the outcome of their hiring decisions.