http://dev.jquery.com/changeset/6442

isObject: function( obj ) { 
  return this.constructor.call(obj) === Object; 
}, 

I might be missing something but after staring at this for a while, still seems to be quite odd:

-- First, this is a static method, in which using this is quite dangerous, as someone might save the function in a local variable, where this will be a reference to the window object

-- this here basically refers to jQuery

-- so this.constructor refers to Function

-- you call it in another context and it will return Object, the Object constructor???

If it's not just a typo I'd be really curious how is this supposed to work :)