
Multiple virtual screen window management systems really need to figure out what to do when using external monitors. Currently, all such systems (including Apple's Spaces) simply multiply the number of virtual workspaces by the number of physical screens. However, using an additional physical screen is distinctly different from using several invisible virtual ones: physical screens are used for multiple simultaneous attentional areas, but virtual screens can only be used when intentionally switching attention.
Sometimes, virtual screens are used for peripheral attention, with the help of notification systems like Growl, but that is often the case because an extra physical screen is not available. Most virtual workspace managers have options to auto-position application-specific windows onto a virtual screen. That's great for when the number of physical screens never changes, but ends up using less display real-estate when switching from one screen to two (as in the case of laptops with an external monitor).
What is really needed is closer to attention to how people position paper and other information displays on a workspace, and design positioning algorithms around that. For instance, the sketch above shows a window manager automatically moving a specified window from invisible (1) to peripheral (2) space when an external monitor is attached.
More reasons for field research in user experience work...
Update: I hunted through the CHI and related archives, and found only one work that looked at window management strategies & multiple/virtual desktops empirically:
Ringel, M. (2003). When one isn't enough: an analysis of virtual desktop usage strategies and their implications for design. In CHI '03 extended abstracts on Human factors in computing systems (pp. 762-763). Ft. Lauderdale, Florida, USA: ACM. doi: 10.1145/765891.765976.
and two others that compared usability in terms of space usage and task switching:
Hutchings, D. R., Smith, G., Meyers, B., Czerwinski, M., & Robertson, G. (2004). Display space usage and window management operation comparisons between single monitor and multiple monitor users. In Proceedings of the working conference on Advanced visual interfaces (pp. 32-39). Gallipoli, Italy: ACM. doi: 10.1145/989863.989867.
Truemper, J. M., Sheng, H., Hilgers, M. G., Hall, R. H., Kalliny, M., & Tandon, B. (2008). Usability in multiple monitor displays. SIGMIS Database, 39(4), 74-89. doi: 10.1145/1453794.1453802.
Most of the others were, unfortunately, proposals for new/redesigned window systems based on task/action level inspiration. Some, like the Hutchings [1] paper, and BumpTop suggest new window management actions: this still ignores the role of the computer in organizing windows, and pays more attention to user-initiated actions. While there are works on spatial memory, attention and activity-based window organization [2] I couldn't find anything that puts information organization, task/activity structure, memory & attention, and object/window manipulation together to treat the desktop as a workspace. Interesting how the metaphor lost almost all salience in translation...
What's interesting is that work I did on workspaces while at Steelcase informs most of these issues, even though we were not remotely aiming for that. I guess I'll just have to write a CHI paper, then.
References
Chapuis, O., & Roussel, N. (2005). Metisse is not a 3D desktop! In Proceedings of the 18th annual ACM symposium on User interface software and technology (pp. 13-22). Seattle, WA, USA: ACM. doi: 10.1145/1095034.1095038.
[1]Hutchings, D. R., & Stasko, J. (2002). QuickSpace: new operations for the desktop metaphor. In CHI '02 extended abstracts on Human factors in computing systems (pp. 802-803). Minneapolis, Minnesota, USA: ACM. doi: 10.1145/506443.506605.
Hutchings, D. R., & Stasko, J. (2004a). Revisiting display space management: understanding current practice to inform next-generation design. In Proceedings of Graphics Interface 2004 (pp. 127-134). London, Ontario, Canada: Canadian Human-Computer Communications Society. Retrieved June 16, 2009, from http://portal.acm.org/citation.cfm?id=1006058.1006074&coll=Portal&dl=ACM&CFID=41002027&CFTOKEN=29749222.
Hutchings, D. R., & Stasko, J. (2004b). Shrinking window operations for expanding display space. In Proceedings of the working conference on Advanced visual interfaces (pp. 350-353). Gallipoli, Italy: ACM. doi: 10.1145/989863.989922.
Khan, A., Matejka, J., Fitzmaurice, G., & Kurtenbach, G. (2005). Spotlight: directing users' attention on large displays. In Proceedings of the SIGCHI conference on Human factors in computing systems (pp. 791-798). Portland, Oregon, USA: ACM. doi: 10.1145/1054972.1055082.
Robertson, G., Czerwinski, M., Larson, K., Robbins, D. C., Thiel, D., & Dantzich, M. V. (1998). Data mountain: using spatial memory for document management. In Proceedings of the 11th annual ACM symposium on User interface software and technology (pp. 153-162). San Francisco, California, United States: ACM. doi: 10.1145/288392.288596.
Robertson, G., Horvitz, E., Czerwinski, M., Baudisch, P., Hutchings, D. R., Meyers, B., et al. (2004). Scalable Fabric: flexible task management. In Proceedings of the working conference on Advanced visual interfaces (pp. 85-89). Gallipoli, Italy: ACM. doi: 10.1145/989863.989874.
Stuerzlinger, W., Chapuis, O., Phillips, D., & Roussel, N. (2006). User interface façades: towards fully adaptable user interfaces. In Proceedings of the 19th annual ACM symposium on User interface software and technology (pp. 309-318). Montreux, Switzerland: ACM. doi: 10.1145/1166253.1166301.
Tashman, C. (2006). WindowScape: a task oriented window manager. In Proceedings of the 19th annual ACM symposium on User interface software and technology (pp. 77-80). Montreux, Switzerland: ACM. doi: 10.1145/1166253.1166266.
[2] Bardram, J., Bunde-Pedersen, J., & Soegaard, M. (2006). Support for activity-based computing in a personal computing operating system. In Proceedings of the SIGCHI conference on Human Factors in computing systems (pp. 211-220). Montréal, Québec, Canada: ACM. doi: 10.1145/1124772.1124805.