Balázs, our issue tracker is designed to be light weight. If you are looking for more complex queries or reporting and performance metrics, you may want to consider JIRA + Greenhopper for more heavy duty work with planning and reporting on work.
@Marcus Bertrand That approach is walking a very thin line between up-selling another product and intentionally inconveniencing your client base. Date filtering is a very very very simple and common use for a simple issue tracker. "Light weight", even. Jira is definitely a nice issue tracker, but overkill for most simple projects.