I have the impression that their reputation is strongest for the traditional types of OR-based projects (supply-chain, quant marketing, etc.), as compared to firms like Monitor or Bain who are best-known for branding-based projects.
Efficiency-focussed, OR-based, projects are the popular kind with clients right now, so I see ATK as being positioned to do relatively well in the recession.
Culturally, ATK's reported to be slightly more grounded than MBB, but only slightly. The short period of ownership by EDS wasn't at all popular, for example, and hasn't had a perceptible lasting impact on culture.