Chemistry and eHarmony show you, your similar/shared interests with other persons when you see their profiles.From the Official Blog of eHarmony
August 11, 2009
"Remember, you will still only receive matches based on eHarmony's 29 Dimensions of Compatibility – we don't send you matches based solely on these common interests. That said, when you do receive a match and you do share common interests, you'll already have a great topic on which to strike up a conversation."
and Chemistry uses the new "Hidden Chemistry Weekly Questions" feature, but Chemistry also uses those questions to "improve" your matches.