Okay, let's spend a little time sorting through the Mac Duff file before moving on. Really, this kind of thing takes time to evaluate, even though you'll see some fans bemoaning the move as a failure already.
A few points to consider/discuss.
1. Mack promoted Akina.
The Duffster joins the Texas staff as an "Assistant Head Coach and Co-Defensive Coordinator," which means it was, technically, more or less a lateral move for Akina, but when you consider the full context of the situation, this was, in the end, a vote of confidence in Akina. Based on how this played out, it's clear Mack decided that Akina could be trusted to lead this defense, and that the remaining question was how to find the right complimentary coach to work with the linebackers.
2. Given (1), this move makes complete sense.
Given the decision to keep/promote Akina, Mack had two choices: find a proven linebacker coach to come in and integrate with Akina or hire Mac Duff. Seriously, when you think about it, Mac Duff is uniquely qualified to be Akina's right hand man. The two worked together for a decade in Arizona with Dick Tomey, Mac Duff is a linebacker coach, and the familiarity with each other that the two enjoy means there won't be any awkward "getting to know you" dances at the Alumni Center this month.
3. This is a better hire than a "splash" hit.
Texas has now had four defensive coordinators in five seasons. It's been mostly good, mixed with some bad, but despite the relative success Mack's had bringing in some of the guys he has, it sure would be nice to have a little stability in the system. In that regard, this is a lot better than bringing in a(nother) guy that will continue the trend of one to two years at Texas before seeking a promotion at another school. Akina loves Austin, his family is happy here, and Mac Duff is not in a position where he's coming here as a stepping stone to something else. Assuming all goes reasonably well, Texas should have this tandem in place for a nice multi-year run. I don't think that should be underestimated.
4. Duff Dog can coach special teams.
Larry Mac Duff has a ridiculously good record coaching special teams - something that shouldn't be overlooked in this hire. Mack Brown likes for all the coaches to chip in to special teams coaching. Having the Duffster around for that will only help. It's not THE reason to hire him, but it's a nice plus. Something worth remembering.
5. His repuation with linebackers es bueno.
Duff's reputation is as a coach that breeds ferocious, attacking linebackers. After the disaster that was 2005, this is a welcome change. I loved Chizik for a number of reasons, but his "stay within the base 4-3 at all costs" mentality hurt the '06 team. Sorry, but it did. I liked the defensive gameplan in the Alamo Bowl (called by Akina) a LOT more than I liked the Chizik gameplan against, say, Kansas State. (Josh Freeman just completed another touchdown, btw) Akina and Mac Duff are more aggressive than Chizik; for all that Chizik did well, at times he was a bit of the anti-Carl Reese. Perhaps -too- cautious. Probably best of all, Akina will (hopefully) be a bit of both: a desire to take more risks to get pressure on the quarterback, but a commitment to staying within that disciplined base that served Chizik so well.
6. Recruiting still matters.
Ditching Akina would have made a lot of players unhappy. By all accounts, it would have been a problem. So we keep Akina, bring in a guy with college and NFL cred, and keep our recruiting machine rolling. Considering the enormous risks with the alternative solution, this looks to me like one heck of a good decision by Mack. Time will tell.