Kudos for writing this introduction!
Purpose: Depending on that the purpose of this is -- to learn Perl programmers to program in Haskell or learn Perl programmers Haskell's techniques -- different comments will follow. Perhaps you should state the purpose of the document clearly in the -1 chapter, other than that it may be interesting?
Density: As always with introductions it's hard to make everyone happy. I was happy as it was a quick re-cap for me as I already know basic Haskell. But I think it may be a bit too dense for the average Perl programmer, especially with the strange syntax.
Syntax: A function call in Haskell looks quite differently and the precedence is different too. As you have in your example, factorial n = n * factorial (n - 1). Those parenthesis there are unnecessary to a Perl programmer. Also, two-argument functions don't use commas, which also look strange to a Perl programmer. A paragraph on the key differences in syntax may be worth its space, and then you can move the comment about the significant indenting to a more logical place. Idealy, you wouldn't have to spend time on explaining syntax, but I think that's can't be avoided successfully.
Useful tools: I liked learning Haskell because it gave me some new cool ideas about programming languages and tools I'd like to be able to use in Perl. I think that a document like this should focus the most on parts of Haskell that may be truly hands-on useful to Perl programmers and explain other parts just enough to make the Perl relevant parts understandable. Hopefully, this will get Perl programmers even more interested in Haskell as they see applications of what they read here. Depending on your purpose you could perhaps retitle it to "Haskell idioms/design patterns in Perl" or write a sister document called that?
Perl examples: Perhaps every Haskell example could be accompanied with a Perl translation, or something that goes as close as possible? That way Perl programmers may more easily relate to the Haskell code.
Hope I've helped,