I hope the query on the "suggestion" is not what's in place; it's terribly inefficient. For starters, "FROM shares,users" is doing a left join which takes exponentially more resources than the appropriate inner join.
Suggested in
http://pastebin.com/TQ206qQj:
SELECT users.username,COUNT(shares.*) FROM shares,users WHERE time<=FROM_UNIXTIME(1389867642) AND our_result='Y' AND users.userid=shares.userid GROUP BY shares.userid;
Much more efficient query:
SELECT u.username, COUNT(s.id)
FROM shares s
INNER JOIN users u ON u.userid=s.userid
WHERE s.time<=FROM_UNIXTIME(1389867642) AND s.our_result='Y'
GROUP BY s.userid
Note that this assumes that the shares table has an "id" column referenced in the COUNT operator. Doing a COUNT(*) also burns up unnecessary resources; it should be COUNT({unique column})
You might want to pastebin this and tweet the link to him. Otherwise, he won't be seeing it among all the other craptalk that goes on in this thread (including mine at times). Might want to ask for an explain plan afterwards, I curious how it will turn up if he agrees to implement it.