Instead of using geocoder and fetching the info from a 3rd party web service, you could use a local installation of the geoip database from maxmind and the geoip-c gem.
Maxmind's database is 1) huge in filesize 2) not as extensive as some 3rd parties (like Google, Yahoo, and Bing), and 3) updated monthly which adds another task to your workflow.
Given that the example use is to track where clicks are coming from, those three sound like dealbreakers.
I've had almost the opposite experience: reading ERB (or JSP or whatever) is a giant pain in my ass since it frequently isn't maintained with consistent indenting and formatting. I like that HAML forces that on you.
Extra dependency that I buy. But narrowing filter for hiring? Seriously? Any web developer should be able to pick up any of these templating languages (as well as CSS preprocessors such as less, sass etc) in less than a day.
Why oh why do people throw non-default templating languages into their tutorials when it's not relevant to the tutorial at all?
When you write your views in ERB, your tutorial's accessible to everyone who's used Rails, and the HAML / Slim / Mustache / Liquid / whatever people can convert them over easily. When you write your views with something other than ERB, someone who's only familiar with ERB has a much harder task, especially if they're new to Rails and don't know much about alternate templating languages.
https://github.com/mtodd/geoip