Admittedly, this may be more of an observation than hint. On most full screen apps I use (Reeder for Mac, Mail, the fugly iCal) you don't typically need another window.
I have always had Safari to open new windows as tabs. I think this may now be the default in full screen mode. If you want another full screen invocation of Safari, just hit Command+N.
By extension: each Safari window with its own set of tabs can independently be in full screen mode or not.
[crarko adds: This doesn't actually run a second copy of Safari, it just creates a new Space and puts the new full screen window in it. It looks like Preview does something similar when you open multiple documents while running full screen.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20110729091812717