Previous exposure to an SSRI/SNRI increases the initial efficacy and decreases the amount of time it takes the medication to start taking effect on the the serotonin or norepinephrine ruptakes.

Also, your examples include:
1) A single patient on 20mg of Celexa.
2) A single study spanning a total of 83 test subjects
3) A doctor saying that some people may experience a "poop-out effect" (very professional wording) but the entire article explains how it can be attributed to a multitude of other factors.

So I'll stick with my original statement.