When the restart tries to quit the Terminal application, Terminal will yell at you and give you the option to cancel, which, if you select it, will cancel the logout altogether and let you restart when you feel like it.
This is unlike OS 9, which would allow you to delay a restart in order to save a document or close a connection in a telnet app, etc., but would continue the logout as soon as you quit the offending application.
[Sudo Editor's Note: You should really restart your machine if asked by an installer, as certain system functions may not perform properly until you do so.]

