According to the babel package documentation (section 64), the default font used for Hebrew is Jerusalem which is a Metafont. Bold text is set in Dead Sea.
This results in weird looking text, such as this:

Notice the first two words from the right on the second line. Ideally it should look like this:

(unfortunately the author of that doesn't remember the settings he used)
I looked to no avail on how to set the bold font so it appears like the regular one only in bold.
As a last resort, I tried migrating from babel to XeTeX with bidi, but couldn't set the font (using fontspec) to the jerus10.mf file that comes with the babel package. Maybe if I could get a hold of a TrueType font that matches it.
EDIT: Here's a minimal example that illustrates the problem:
\documentclass[a4paper]{article}
\usepackage[utf8x]{inputenc}
\usepackage[english, hebrew]{babel}
\begin{document}
שלום
\emph{שלום}
\bf שלום
\unsethebrew
Hello
\emph{Hello}
\bf Hello
\end{document}
Which gets rendered like this:


hebrew(which also shows some of the problems). Don't try to use the original metafont - try to find an otf/ttf version of your jerusalem font (as far as I can see it shouldn't be to difficult). – Ulrike Fischer Nov 22 '11 at 9:25