In the last two weeks, one of the best-known of TV tropes, the Flashback, was used in a number of TV shows:
'Brothers & Sisters'
'In Plain Sight'
And that's not even mentioning 'Cold Case', where the flashback is standard with every episode. (And the producers take care in the casting of the actors so that if they play the same role separated by decades, they at least look like each other.)
'In Plain Sight' usually begins with a flashback to show how the witnesses ended up in protection. However, with the episode that dealt with how Mary first met Marshall and then joined WITSEC, the flashback sequences ran throughout.
Most shows deal with flashbacks eventually; it just seemed strange to have a cluster of them being aired so closely together.