Are there any plans on improving count(*)'s speed?

[Manuel Aude]

I decided to give InnoDB a try, mainly because I care about integrity and being able to have true relations. Now, simple queries like:

SELECT u.id, u.username, y.difboards
FROM (
SELECT user_id, count( DISTINCT board_id ) AS difboards
FROM messages
GROUP BY user_id
ORDER BY difboards DESC
LIMIT 0 , 30
) AS y
inner join users u on u.id = y.user_id

That used to take 3 seconds (4.6 million rows in messages table) take a reaaaally long time. I had already denormalized the table for that query (3 seconds is too much for any user), but to avoid that kind of queries, I denormalized the DB even more, which shouldn't be necessary.

Why is it necessary to lack the speed of MyISAM for counts?