Collection (acquiring the information) is the easy part.  Machine processing (e.g. keyword recognition, both spoken and written; voiceprint recognition; email sender & receiver ID matching) comes next and deliberately has it's false-positive ratio set slightly on the high side.  

Then comes post-processing which is where humans get into the picture.  NSA's foreign intel activities require a very large number of humans to listen to snippets of conversations and read snippets of email, and judge them "go / no-go" quickly.  The stuff that gets "go" proceeds to the next step where someone listens to or reads more of it up to & including the entire thing.  From there, anything that gets a further "go" proceeds to analysis.  Analysis is where they expand the scope as needed to get full context (i.e. bring in other intercepts with similar header information or call detail information) and develop the original intercept into a piece of usable intel.  

The steps that require human intervention (preceding paragraph) are enormously labor intensive, not even NSA can keep up with the flood.  FBI has fewer resources than NSA.  FBI isn't allowed to ask NSA to pick up part of their (FBI's) workload except in extraordinary circumstances (e.g. terrorist attack immanent or in progress).  So FBI has a huge backlog to deal with, and has to compensate for the high false-positives on the machine side by using a deliberate low false-positive threshold on the human side.

The amount of traffic that can be collected by machine intercept is absolutely enormous.  But that is not the point.  The amount of traffic that can be processed by live humans is a tiny trickle of what can in theory be collected.  And the storage capacity that would be required to store all of what's collected to enable the humans to catch up, is beyond even NSA's budget.  

By analogy, the reason that dial phones became universal was that the Bell System realized that there were not enough people in the workforce who could be hired as operators to put through calls on manual switchboards.  That was over 60 years ago.  Compare the volume of communications today, to 60 years ago.

Bottom line here is, there is relatively little to worry about in terms of civil liberties issues in a practical sense.  However it's always a good idea to keep track of these issues in the event there is ever an abuse or misuse of the capabilities.  

And of course, encrypt, encrypt, encrypt, the longer the key-length the better.