Tom, the /o/$object_id is merely a replacement for the site_node.get_url function if you want to create lists of links. It defers the expensive process of calculating the URL. The assumption here is that there fairly many pages in a web system that show fairly many links. Take portal: a regular portal page may show 5 portlets with 10 links each. Your site calculates 50 URLs although the user can click at most only one at a time.
On an Oracle-backed OpenACS system with 329 site nodes this is the price:
SQL> -- gee, no bind vars
select site_node.url(node_id)
from site_nodes where object_id= 93013;
Statistics
----------------------------------------------------------
5 recursive calls
0 db block gets
12 consistent gets
site_node.url is a recursive function that gets more expensive the more nodes you add.
In short /o (or LC_$ISOCODE/o) would supersede most calls of site_node.url thus saving overall load on the system and will not compromise security.
