We report how users interact with an experimental system that transforms single-field textual input into a multi-field query for an existing travel planner system. The experimental system was made publicly available and we collected over 30,000 queries from almost 12,000 users. From the free-text query log, we examined how users formulated structured information needs into free-text queries. The query log analysis shows that there is great variety in query formulation, over 400 query templates were found that occurred at least 4 times. Furthermore, with over 100 respondents to our questionnaire, we provide both quantitative and qualitative evidence indicating that end-users significantly prefer a single field interface over a multi-field interface when performing structured search.