Interesting question. To be honest I'm kind of on the fence with AR. It makes trivial SQL very simple but I find myself forced to drop down all the time into raw SQL for a lot of cases and I also find that AR queries with a lot of options (order, group, select, limit etc) aren't much of an improvement in readability or abstraction over the raw SQL.
What's more, I finally gave up after a year of waiting for this pretty fundamental bug in the postgres driver to be fixed and finally just hacked around it: https://rails.lighthouseapp.com/projects/8994/tickets/2622-p...