In MTG, what happens when Sakashima the Imposter copies Halcyon Glaze?
A relevant paragraph from the MtG Comprehensive Rules:


  706.2. When copying an object, the copy acquires the copiable values of
  the original object's characteristics
  and, for an object on the stack,
  choices made when casting or
  activating it (mode, targets, the
  value of X, whether it was kicked, how
  it will affect multiple targets, and
  so on). The "copiable values" are the
  values derived from the text printed
  on the object (that text being name,
  mana cost, card type, subtype,
  supertype, expansion symbol, rules
  text, power, toughness, and/or
  loyalty), as modified by other copy
  effects, by "as . . . enters the
  battlefield" and "as . . . is turned
  face up" abilities that set
  characteristics, and by abilities that
  caused the object to be face down.
  Other effects (including type-changing
  and text-changing effects), status,
  and counters are not copied. Example:
  Chimeric Staff is an artifact that
  reads "{X}: Chimeric Staff becomes an
  X/X artifact creature until end of
  turn." Clone is a creature that reads,
  "You may have Clone enter the
  battlefield as a copy of any creature
  on the battlefield." After a Staff has
  become a 5/5 artifact creature, a
  Clone enters the battlefield as a copy
  of it. The Clone is an artifact, not a
  5/5 artifact creature. (The copy has
  the Staff's ability, however, and will
  become a creature if that ability is
  activated.) Example: Clone enters the
  battlefield as a copy of a face-down
  Grinning Demon (a creature with morph
  {2}{B}{B}). The Clone is a colorless
  2/2 creature with no name, no types,
  no abilities, and no mana cost. It
  will still be face up. Its controller
  can't pay {2}{B}{B} to turn it face
  up.


I think that what this implies is that Sakashima does NOT become a 4/4 creature when copying a creatured-up Halcyon Glaze, but rather an enchantment with Halcyon Glaze's rules text.  So you'd have to cast another creature to turn enchantment-Sakashima into a 4/4 flyer.  I don't think he'd revert to being a 3/1 at end of turn; he'd stay a noncreature enchantment until returned to hand with Sakashima's ability.

Essentially the key issue here is about what the Magic rules like to call "copiable values". The switched-on Glaze is a valid thing for Sakashima to copy, because it's a creature in play, but its switched-on status is not a copiable value. So Sakashima just becomes a switched-off Glaze, with all the extra characteristics as defined in the Sakashima rules text.