by definition its the difference between the level of harm it could cause national security if it were leaked. the difference between the two is determined by the classifier. believe it or not two completely unclassified documents or pieces of information, when combined together, could become top secret. conversely a snippet of top secret data taken in a report might be entirely acceptable as unclassified. it really depends. check out my earlier post on derivative.
there are surely cases where undocumented information never gets made public. for example the taste of the lubricant on a hind helicopter? its important to remember that the goal is to reduce and limit the total amount of classified data in general. if it doesnt need it, and its reviewed, then it never gets classified. the weather in Iraq for example.
there are rare situations where you can extend 10, or 50 years a classified designation. its got to be demonstrably needed. the data must be dangerous enough or important enough that more than just you and your boss agree its 'classified.' these extensions get shot down at a non trivial rate. as best im aware, you cant just call something classified 'forever.'
foreign partnerships arent uncommon. in the case of >>34950
it depends on what youre doing. its highly subjective. ive had taxi rides that were abrupt and uncomfortable because we openly admitted we couldnt talk in front of an ethnic driver who may be a foreign national.
information seeking: pass. sorry.
journalists are good at finding declassified documents! generally its GAO or administrative reports. again, declassified information is 99% very boring. ask your local newspaper or submit a FOIA...you would be amazed how effective those are.
uh at home? I run whatever i decided to pack into my lian li. at work its dell/HP/Lenovo and whatever made the budget. again: not hollywood :P
i hate raid, but im more of a performance guy.
[quietly ignores data questions]
as for longevity youre asking the wrong guy. i routinely just blow everything away because i dont care. i run linux at home, multifactor auth too. did you know you can make your own CAC cards? build a CA authority. its seriously fun.