The xelatex with biblatex can generate raggedright bibliography by means of
\raggedright\printbibliography
but adding hebrew to polyglossia:
\setotherlanguage{hebrew}
disables this functionality, i.e. the Bibliography is justify to the margins and hyphenation works.
How to switch off the hyphenation in the Bibliography with the hebrew working?
Typically you should customize the bibliography layout by modifying \bibsetup. However the bidi package, loaded by polyglossia with RTL languages, redefines \raggedright. This new definition has no effect on list items when issued outside the list environment. So the problem you see with \printbibliography also applies to enumerate and itemize.
To cope with this, you can invoke \raggedright inside the list environment. For bibliography environments in particular add to your preamble:
\AtBeginBibliography{\raggedright}
Otherwise you can save the original definition of \raggedright before loading polyglossia.
\let\origraggedright\raggedright
\usepackage{polyglossia}
The original \raggedright can be issued in the document body, before \printbibliography:
\origraggedright
\printbibliography
or in \bibsetup:
\appto{\bibsetup}{\origraggedright}
\raggedrightworks correctly in normal paragraphs. – egreg Dec 23 '12 at 17:25\printbiblioraphyto set its own paragraph alignments? I suggest you consult the biblatex documentation about this. – einpoklum Dec 24 '12 at 11:40