SIL International ("working for more than 50 years to study, develop and document the world's lesser-known languages") has some great information about complex writing systems of the world:

• Examples of Complex Rendering shows some of the tricky manipulations that need to happen for correct rendering, including glyph shape changes, glyph reorderings, ligatures, and so on.
• Challenges in publishing with non-Roman scripts demonstrates more difficulties, at the sentence, paragraph and page level.

There's ton of other interesting stuff on the site about Unicode, font technologies, input techniques, type design, and so on.