The default font for Hebrew text in Open/Libre Office on Windows is Tahoma. It shouldn't be - it's a reasonable sans-serif font for dialogs and menus, but for a document's body text the default should be a serif font. For Latin it's Times New Roman. Microsoft's Times New Roman has a Hebrew part, which is a reasonable and common font for documents in Hebrew. That is the default in Microsoft Office, too.
(Of course it would be better to have a uniform and freely licensed font in LibO on all platforms, but until that happens, if Times New Roman is good for Latin, it should be good for Hebrew, too.)
Please identify what need to be changed and propose the font names in the preferred order. Thanks!
Updated link, as there were some changes in the source tree (libs-core -> core):
A friend with 3.5.0 beta1 says he got times new roman as the default Hebrew font on Windows, not Tahoma. For Linux that's Nachlieli (if culmus fonts are installed).
Testing on Windows 7 (without office) gave me Tahoma for Hebrew. Removing the font from the font list on main.xcd changed it to Miriam.
Fixed in master the libreoffice-3-5 branch. Will verify in 3.5.0 beta3.