So I poked around in the application contents, and found that the bulk of the size is indeed the templates -- but multiplied because of how they were built. Each template is localized for all of the supported OS languages, with a complete set of files (including sample images) duplicated in each. But the only way to take advantage of, say, the French version of the Formal - Welcome page (i.e. Formel - Bienvenue) is to change your system language in the International preference pane and restart iWeb. This also changes the application menus, so it doesn't really make sense unless you're running that system language all the time anyway. And to top it off, most of the site is already greeked anyway, so the only things localized are maybe the page name and the tag of "Created on a Mac" (or, "Créé sur un Mac" for our example).
So, unless you're really stuck for how to say Blog in Swedish (which, incidentally, seems to be 'blogg') or the like, you can save space by removing all but your active language from the iWeb application bundle. Control-click on the app and choose Show Package Contents from the pop-up menu. Then go into Contents/Resources, and delete all of the *.lproj folders except for the language you use (e.g. English.lproj). Total savings should be about 520MB.
[robg adds: Read on for more details on how the various iLife apps store their themes, as well as my method of saving space while keeping a backup copy of the trashed files.]
I noticed after upgrading to iLife '06 that a few of the apps had grown significantly in size, presumably due to the inclusion of theme files within the application itself, rather than broken out in Application Support as had happened with iDVD. I checked to see whether it was possible to move the Themes from inside iPhoto 6 to where I assume they'll be eventually (Application Support/iPhoto/Themes), but any files moved would no longer appear in iPhoto's Book template selection, even with aliases in place. Oh well, maybe it will change in iPhoto 7 when they add the inevitable additional templates.
iWeb was a different story. The themes weren't stored together as they are in iPhoto, or were in older iDVD and Keynote versions. Rather, they're bundled into each language project, so each language has its own localized version of each page in each template. Needless to say, this adds up -- I figured that by removing all of the inactive language templates, the application would shrink by 520MB (hence the hint).
Overall, while three apps added some form of template support (GarageBand for recording session types, iMovie's moving themes, and the new iWeb page templates), their approach to a common storage model is still haphazard. At present:
- GarageBand: project files (*.band) in new Templates folder in /Library/Application Support/GarageBand/Templates -- includes options for "Movie Score" and "Podcast Episode."
- iDVD: theme files (*.theme) are organized by version they were added with, in /Library/Application Support/iDVD/Themes (iDVD v3 through v6 only; v1 and v2 are still absent).
- iMovie: theme bundles (*.bundle) are stored in /Library/Application Support/iMovie/Themes (no hierarchy).
- iPhoto: book templates (*.IPBookTheme) are now bundled into the application, in Content/Resources/Themes, ballooning the file size by about 300MB.
- iTunes: no themes (unless some remnant of the SoundJam Skins support remains).
- iWeb: the real oddball, templates (*.webtemplate) are stored in each language project folder within the app (e.g. Travel template for "About Me" page in English is in Content -> Resources -> English.lproj -> Templates -> About Me -> Travel About Me.webtemplate).
The trend in iWeb/Pages is worrisome, if only because it makes the addition of themes in later versions (a safe prediction) an exponential waste of space. I think both of their template formats will need to be inverted at some point, with shared files (images, scripts, etc.) stored only once, and then the localized strings stored in separate language subfolders as is more the norm.
Again, as with the system installer packages, it's curious how splintered the formats remain among similar applications -- solving the same problems different ways, and changing from version to version. Testament perhaps to the size and complexity of programming something like the modern iLife suite.
[robg adds: I'm always hesitant about deleting things from applications, even something as seemingly safe as language files. So I did this slightly differently for both Pages and iWeb. First, I selected the program in the Finder, then hit Command-I to open a Get Info window. I opened the Language section of the window, and then unchecked all languages other than English. This deactivates the languages without deleting them, but will not (as of yet) save any disk space.
Then I control-clicked on the application and drilled in via Show Package Contents to the Contents folder. The deactivated languages are now all grouped together in a folder named Resources Disabled inside the Contents folder. I moved this folder to a backup disk, and changed the name (Pages_Resources Disabled and iWeb_Resources Disabled) so that I have them available in the event of an emergency. Finally, I deleted the Resources Disabled folders from within each application.
I tested both apps after making the change, and both worked just fine. Total space saved: 1.08GB, and I have peace of mind at the cost of that same 1.08GB of space on my backup drive.]

