As I promised, here is the evaluation of redoing a site from ERB to Haml. To immediately cut to the chase: Haml IS worth it!

• It's so definitely faster and easier to write than ERB.
• Your HTML output is nicer.
• Partials rendering with the right indentation automatically.
• It forces you to take a good look of what you're actually making.
• Because it's so strict on it's syntax, you will be using more helpers and custom model methods, which is a good thing.
• No more forgetting to close a div and spending hours to find out which one.
• Faster refactoring because of less code and easier to read.

There are some downsides however. I'd rather not talk about the hours I tried to fix some idiot problem with partials and the locals option. Just use locals as less as possible, preferably not at all. Some cons:

• Yet another syntax to be learned.
• Errors with Haml syntax are a bit harder to locate, but you'll make less after you encountered a few.
• A gem needs to be installed on the server, which can be difficult if you don't have root rights on the server
• The syntax highlighter on VIm is not quite up to it.
• Rails helpers screw up the nice HTML Haml creates for you. The form_tag helpers for example.

So if you are starting a new project, or redoing the entire HTML of you're application: try Haml! Chances are you'll like it!