Is there a way to

[dippin' low]

See how many users are using each skin on my board? Besides individually going through accounts and checking what they're using.

[Lats]

Try this query...

SELECT 
    styleid, 
    count( styleid ) AS HowMany
FROM 
    user
GROUP BY 
    styleid

[Zachery]

Also note that this will only take into account what styleid they have selected inside of the usercp, not the style they are actually using most of the time.