Social tagging is a widespread activity for indexing user-generated content on Web services. This paper summarizes research on folksonomies and their retrieval effectiveness. A TREC-like retrieval test was conducted with tags and resources from the social bookmarking system delicious, which resulted in recall and precision values for tag-only searches. Moreover, several experimental tag-based databases (i.e., power tags, Luhn-tags) have been tested regarding their retrieval effectiveness. Test results show that folksonomies work best with short queries although recall values are high and precision values are low. Here, a search function “power tags only” greatly enhances precision values.