iCal's Debug menu in Lion has a 'Top Sekret' (sic) menu item which allows you to increase the number of days in the Week view up to 28.
You have to turn on the Debug menu in iCal first. This was detailed previously on MacOSXHints for 10.5 and is done with the following Terminal command:
defaults write com.apple.iCal IncludeDebugMenu 1
Or you can use Secrets from Blacktree, a System Preferences pane where it's simply a checkbox.
The Debug menu in iCal now features a 'Top Sekret' menu item. And you can alter the number of days in the week view between 7, 14, 21 and 28. You'll likely need a widescreen monitor or two for that.
[crarko adds: This is definitely new in 10.7. To turn the Debug menu off repeat the above command, using 0 instead of 1.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20110905085755821