After using Act of Treason and Cloudshift, does a creature re-enter the battlefield under my control?
It works just as you hope.

Previous "flicker" effects returned the target to play "under its owner's control".  Cloudshift returns it to play "under your control".

Act of Treason gave you control of the creature, making it a valid target for Cloudshift.  Cloudshift returns it into play under your control, and with no memory of its previous life as either the opponent's creature, or of having had Act of Treason cast on it.  It's yours for keeps, or at least until the game ends or another control-changing effect takes place...


  611.2a A continuous effect generated by the resolution of a spell or ability lasts as long as stated by the spell or ability creating it (such as “until end of turn”). If no duration is stated, it lasts until the end of the game.