I've not used the Rails ORM so I can't comment on how good it is or how easy it is to debug queries (peer behind the magic).
*The ORM automates things like tersely expressing the object associations I've built, leaving room for fewer syntax mistakes.'
Maybe it depends on the system you're working on however mitigating syntax errors seems like a small benefit. For me the SQL for most projects is fairly static i.e. once a given set of queries has been defined and tested they can lie there untouched, so once I nail a query and it performs the way I like I hardly ever need to go back and touch it again. However the performance penalty of sitting behind an ORM is ever present, for each query (at least for a cache miss). Personally I just don't like having 100s of lines of code sitting between:
model->get(('model.field' => 'value'));
and actually receiving the data.
It just seems so.... unnecessary.
of course YMMV, and perhaps the benefits kick in when you're working in a team (I'm not).