Username or EmailPassword
VirtualBox is actually also a good example of the negative sides of relying on a cross platform toolkit: while it draws the widgets using native routines, the layout of the widget does not conform to the UI guidelines. Mac OS X specifies a certain distance that widgets are supposed to keep from window borders and other widgets. Qt or wxWidgets do not enforce these distances, nor do they enforce the default type faces or sizes.
By violating the layout guidelines, an application can draw using native widgets but still look alien to a Mac user.