A BIMONTHLY PUBLICATION OF ACM

PUBLICATIONS BOARD

Co-Chairs: Ronald F. Boisvert and Holly Rushmeier Board Members: Gul Agha, Michel Beaudouin-Lafon, Jack Davidson, Nikil Dutt; Carol Hutchins, Ee-peng Lim, M. Tamer Ozsu, Vincent Shen, Mary Lou Soffa, Ricardo Baeza-Yates

PUBLICATIONS OFFICE ACM, 2 Penn Plaza, Suite 701 New York, New York 10121-0701, USA +1-212-869-7440 FAX: +1-212-869-0481

EDITORS-IN-CHIEF

Richard Anderson & Jon Kolko

GROUP PUBLISHER

Scott Delman

EXECUTIVE EDITOR Diane Crawford MANAGING EDITOR Denise Doig ART DIRECTOR Andrij Borys ASSOCIATE ART DIRECTOR Alicia Kubista ASSISTAN T ART DIRECTOR Brian Greenberg PRODUCTION MANAGER Lynn D’Addesio Kraus COPY EDITOR Kate Crane

SUBSCRIPTIONS

Various subscription rates are available; please see the interactions Website at http://interactions.acm.org/subscribe.php for more information.

FORUM EDITORS Lifelong Interactions: Alison Druin On Modeling: Hugh Dubberly Sustainably Ours: Eli Blevis Timelines: Jonathan Grudin Under Development: Gary Marsden

Single copies are $13.00 to members, $20.00 to nonmembers. Please send orders prepaid plus $4.00 for shipping and handling to ACM, General Post Office, P.O. Box 30777, New York, NY 10087-0777 or call +1-212-626-0500. For credit card orders, call +1-800-342-6626. Order personnel available 8:30-4: 30 EST. After hours, please leave message and order personnel will return your call.

(P)REVIE W EDITOR Alex Wright

COLUMNISTS Ps and Qs: Elizabeth Churchill The Way I See It: Don Norman True Tales: Steve Portigal

CHANGE OF ADDRESS

acmcoa@acm.org

For other services, questions, or information: acmhelp@acm.org

CONTRIBUTING EDITORS

Elaine Ann, Dave Cronin, Ame Elliott, Marc Rettig, Katie Minardo Scott, Lauren Serota, Molly Steenson, Mark Vanderbeeken

IN TERACTIONS ADVISORY BOARD Jonathan Arnowitz, Michelle Berryman, Apala Lahiri Chavan, Shelley Evenson, Richard Grefé

ACM Copyright Notice

Copyright © 2009 by Association for Computing Machinery, Inc. (ACM). Permission to make digital or hard copies of part or all of this work for personal or classroom use is granted without fee provided that copies are not made or distributed for profit or commercial advantage and that copies bear this notice and full citation on the first page. Copyright for components of this work owned by others than ACM must be honored. Abstracting with credit is permitted. To copy otherwise, to republish, to post on servers, or to redistribute to lists, requires prior specific permission and/or fee. Request permission to publish from: Publications Dept., ACM, Inc., Fax +1-212-869-0481 or email permissions@acm.org

FOUNDING EDITORS

John Rheinfrank & Bill Hefley

interactions (ISSN 1072-5220) is published six times a year in January, March, May, July, September, and November, by the Association for Computing Machinery, Inc., 2 Penn Plaza, Suite 701, New York, NY 10121-0701. Periodicals postage paid at New York, N Y 10001 and at additional mailing offices. POSTMASTER: Please send address changes to interactions, ACM, 2 Penn Plaza, Suite 701, New York, N Y 10121-0701.

PLEASE VISIT OUR WEBSITE

http://interactions.acm.org

Month + Month YYYY

EDITORIAL INFORMATION

To contact interactions, email our editors at eic@interactions.acm.org, or mailbag@interactions.acm.org

The EiCs generally respond to inquiries, including responses to unsolicited manuscripts, in 2-3 weeks.

For other copying of articles that carry a code at the bottom of the first or last page or screen display, copying is permitted provided that the per-copy fee indicated in the code is paid through the Copyright Clearance Center, 222 Rosewood Drive, Danvers, MA 01923, +1-978-750-8400, +1-978-750-4470 (fax).

ADVERTISING ACM Advertising Department 2 Penn Plaza, Suite 701, New York, N Y 10121-0701 (212) 869-7440 FAX: (212) 869-0481

DIRECTOR OF MEDIA SALES Jennifer Ruzicka jen.ruzicka@acm.org