Been running my current system since July, Wintel, Windows 7 & CS5. Zero issues. Routine upgrade from ACR 6.5 to 6.6 last week.
All I ever use are DNG's from camera (Pentax K-5s currently). I routinely open lots of DNG's at a time doing rough edits Started hanging randomly in RAW. Sometimes after editing 50 files, sometimes after 5. Tried waiting 1,5,10, 15 minutes, still hung. Purged all cache a couple of times. Helped some but problem recurred. Would start to get slow towards the hang. When shutodwn PS with MS Task Manager, DNG file it got stuck on was corrupted, could not re-open.
System is plain vanilla, just routine MS updates. I worked for IBM PC & Lenovo 11 years IT Architect) understand import of mainitaing clean system. 40 years of IT. Been building PC's since 1986. Read Forums here, installed CS5 on an old PC to get ACR 6.5 Camera Raw 8Bi file. Replaced the ACR 6.6 version.
Since replacing the file, I have been working through thousands of Ballet performance photos from weekend that I really need to get on-line. Six straight hours, not a problem.
Adobe might want to consider some further testing with ACR6.6. I think you all have a Sev 1 defect.