Raimund Dachselt presented FaceZoom, a widget for quick navigation, e.g. for a tree structure . I liked his characterizing “a stacked treemap” - which explains nicely what the widget does and where the efficency can be found. At TEI’08 he gave already a nice private demo on how this can be linked to mobile devices and how to use a off-the-shelf phone with an accelerometer as controller.
 Dachselt, R., Frisch, M., and Weiland, M. 2008. FacetZoom: a continuous multi-scale widget for navigating hierarchical metadata. In Proceeding of the Twenty-Sixth Annual SIGCHI Conference on Human Factors in Computing Systems (Florence, Italy, April 05 - 10, 2008). CHI '08. ACM, New York, NY, 1353-1356. DOI= http://doi.acm.org/10.1145/1357054.1357265