As a backup plan, Randy Ayers is a pretty good hire. He doesn't quite have the defensive pedigree of Tom Thibodeau, but he's pretty close. As an assistant coach under Larry Brown, Ayers helped to preside over a defense that spent four straight years in the top 5 in defensive efficiency (1998/99 to 2001/02). While he failed in his short season as the Sixers head coach in 2003/04, the problem was not Phily's defense, which finished a respectable 10th in efficiency. After two downish years on that front in Orlando, he rebounded to help Orlando finish 7th in defensive efficiency last year, despite not having many great individual defenders. Combine that with his head coaching experience at Ohio State and with the Sixers, and he definitely has a good resume for the position.
Whether this will translate to an improved defense remains to be seen. As good as Ayers' schemes were in Philadelphia, it certainly helped that they had the right personnel to build a defensive-first team. During that four-year stretch, Ayers was able to work with great defenders like Theo Ratliff, Dikembe Mutumbo, Eric Snow, and George Lynch, not to mention Allen Iverson and his ability to play the passing lanes. He doesn't have that same luxury here, although he did prove he could improve a defense even without great defensive players last year.
The only other problem I see with Ayers is that he's not a real take-charge guy. One of the reasons he was fired in Philadelphia was because he was too lax on Allen Iverson, and the two never had a great relationship. I could definitely see a situation where he doesn't make a significant dent on an offensive-minded coaching staff.
Still, I think it's a pretty good hire, considering the circumstances. There's been a pretty good discussion over whether scheming or desire matters more with defense. I'd answer that both were significant problems last year with the Wizards, and both need improving. It's clear that Gilbert Arenas, Caron Butler, and Antawn Jamison in particular didn't try hard enough defensively, a point that Gilbert himself has hinted at. On the other hand, the Wizards schemes were awful, and as cuppettcj said, there were way too many rotation breakdowns that led to open shots. I'd argue that improved schemes can lead to improved desire. Think about it; if your head coach is hollering at you to get tougher, but isn't leading by example with good schemes, the words will ring hollow to a certain degree. One of the reasons the Spurs are so great defensively is that Gregg Popovich puts his players in a position to succeed with a plan. He gives his defenders more defined roles, so that when they mess up and Popovich sits them down, they know exactly what they did wrong. Without a good scheme, Eddie can't really do that, because Eddie can't properly verbalize to the players what specifically needs to improve.
My overarching goal is that Eddie gives Ayers sole authority over the defense, a la Marc Ivaroni in Phoenix. It'll make both guys' jobs easier, and with Ayers pedigree, I'm confident there will be a turnaround. It might not happen right away -- none of Ayers' teams finished in the top half of the league in efficiency in his first year -- but it'll happen sooner rather than later.