[GENERAL] Distinct on a non-sort column

[Cstdenis]

I am trying to write a query that selects recent submissions (sorted by 
submission_date) but only selects the most recent one for each user_id.
example query: /select distinct on (user_id) * from stories order by 
date_submitted desc limit 10;/
However postgres will not allow me to filter out duplicate rows with 
distinct unless I sort on that column, which would product useless 
results for me. Group by seems to have similiar problems, plus the 
additional problem of wanting aggregate functions to be used.
I even tried sorting in a subquery, but it still comes out sorted by 
user_id: /select distinct on (user_id) * from stories where sid in 
(select sid from stories order by date_submitted desc limit 10);/

How can I work around this limitation to get the results sorted the way 
I want, then have the duplicates removed? I can't be the only one 
running into this limitation, there must be some workaround.