Option unicode=true with hyperref
As far as my experience goes, all reasonably recent versions of Adobe's PDF Reader, Gnome's Evince, and Mac OSX's Preview support unicode bookmarks.
I experienced issues with Adobe Acrobat Reader for Linux when the unicode
option was enabled. The displayed page numbers only contained garbled unicode letters. Definitively not a way you want to pass important PDF around.
But this might be reader dependent. The Linux version has some other bugs and so it is likely it is only an issue with this version.
See my comp.text.tex
post about it:
[unicode]{hyperref} results in garbled page numbers in Acrobat Reader 9.4.2 02/11/2011 Linux
The error looks like: