WikiLove is a MediaWiki extension that allows a user to easily create a formatted message on another user's talk page. The purpose is to facilitate people expressing appreciation for one another and leaving "gifts," including barnstars.
There has been research on the effects of WikiLove: Research:WikiLove
In 2012, the community here on Meta-Wiki considered whether to enable the extension here, and decided against.
Pashto Wikipedia (ps.wiki) disables WikiLove for many users with the rationale that «Newbies are misusing wikilove instead using talk pages add new section» (see w:ps:MediaWiki:Common.js). The same on w:mzn: (Mazanderani).