Parsing of class property @inject annotations happens in typo3/sysext/extbase/Classes/Object/Container/ClassInfoFactory.php.
Previously, injectPropertyName() methods were used - but those got replaced with the annotations in http://forge.typo3.org/issues/46598 ("Use @inject instead of inject...-methods").
It seems they slow down TYPO3 by 5%, so the annotations will be replaced again by the inject..() methods: http://forge.typo3.org/issues/54605 ("Inject annotations should not be used by core (~5% performance)")