Look up nodes that reference a given node I'm using the references module (not grounded to it, but it seems to work well enough) however I don't know how in a custom PHP block/etc I would be able to do a query that can look up all the nodes of a given type that reference the current node. 

What sort of query would accomplish this?

For just looking up by type I've used this previously:

&lt;?php
    foreach(node_load_multiple(array(), array('type' =&gt; 'homepage_image')) as $node){
    //code
    }
 ?&gt;
Well, you know, this is one of the problems that gave birth to relation. Nonetheless, an EntityFieldQuery with a fieldCondition('name_of_the_reference_field', 'nid', $nid) is what you want.