Does either have any significant advantages/disadvantages over the other? Just wondering whether I need to switch from my habit of using arrays, since another coder I work with uses objects instead...
From the PHP Manual:
mysql_fetch_object() is similar to mysql_fetch_array(), with one difference - an object is returned, instead of an array. Indirectly, that means that you can only access the data by the field names, and not by their offsets (numbers are illegal property names).
Aside from that, objects tend to be somewhat more expensive (in terms of resource consumption) to use than arrays.