In further failing efforts to fix the problem:
1. I deleted 4 login items and rebooted, each time having the warning appear again (so I've added the login items back):
- EyeTVHelper
- SpeechSynthesisServer
- iTunesHelper
- Dropbox
2. Five times I have rebooted, having the warning appear; each time I:
- opened Activity Monitor,
- sorted items by PID,
- and just couldn't identify a particular process as disappearing when I closed the warning window.
3. DTDunn: I too wondered if the problem could in some way relate to the SSD I'm booting my Mac Pro from. Probably, though, this isn't the source of the problem as my MBP (which boots under the 10.7.4 update) also boots from a SSD and boots without showing the warning window.
As additional info, yesterday I received a phone call from an Apple rep regarding the problem we are all experiencing and sent him (via e-mail) 2 files, the 2nd generated by an app he included: (a) Mac Pro.spx, and (b) an ACCD....tgz file. He said the problem appeared common enough among us Mac Pro users that Apple was investigating. Let's hope a fix appears or we are notified of a fix.
Thanks, again.