Previous versions start up with the last sketch used. V17 doesn't ..
Also it sure would be nice if the app opened with the last window sizes and positions.
This issue seems to be bug of Processing 1.0.3 (base of Arduino IDE-0017).
http://dev.processing.org/bugs/show_bug.cgi?id=837
When exit IDE from File Menu -> Quit or Ctrl-Q, last window size/position and sketch was saved. Even exit from File Menu, sometimes IDE start with default configurations.