Weighting mysql full-text search results by date
A few "small" comments.


Don't use SELECT * for reasons outlined in this question's answers:

What is the reason to not use select *?
Linebreaks and indentation make your code much easier to read:

SELECT *, (MATCH(note) AGAINST (
    '$search' IN BOOLEAN MODE))/SQRT(GREATEST(1, DATEDIFF(NOW(), date)
    )) AS score 
FROM notes 
WHERE userid = '$userid' 
HAVING score &gt; 0 
ORDER BY score DESC



Things I like:


You're not writing it ALL IN SHOUT-CASE ;)