OK, well, not a whole lot. But since I went through and diffed it against CS5, I though I'd share. This is from the Mac perspective.
Some documentation reorganization -- getting-started.pdf moved into docs/guides and whats-new.pdf disappeared and we saw:
./docs/guides:
-feature-development-with-scripting.pdf
+getting-started.pdf
idml-cookbook.pdf
idml-specification.pdf
-indesign-server-plugin-techniques.pdf
-learning-indesign-plugin-development.pdf
-performance-metrics.pdf
+idml-update.pdf
+plugin-programming-guide-vol1.pdf
+plugin-programming-guide-vol2.pdf
porting-guide.pdf
-programming-guide.pdf
-regenerating-java-api.pdf
solutions.pdf
We lost some build frameworks and gained an overview of the idmltools:
./build:
-AdobeOwlContainers.framework
-adobe_epic.framework
-adobe_eula.framework
./devtools/sdktools/idmltools:
+InDesign CS5.5 IDML ReadMe.pdf
It would appear there was a progress bar helper file tossed in with the InCopy applescript scripts for fun:
./scripting/incopy/scriptingguide/scripts/AppleScript/userinterfaces:
+ProgressBar.jsx
We gained scripts for new CS5.5 features and lost LabelGraphics:
./scripting/indesign/samplescripts/AppleScript:
+AnimationEncyclopedia.applescript
-LabelGraphicSupport
-LabelGraphics.applescript
-LabelGraphicsMenu.applescript
./scripting/indesign/samplescripts/JavaScript:
+AnimationEncyclopedia.jsx
-LabelGraphicMenu.jsx
-LabelGraphics.jsx
./scripting/indesign/scriptingguide/scripts/AppleScript/documents:
+ExportEPub.applescript
+ExportEPubWithOptions.applescript
./scripting/indesign/scriptingguide/scripts/AppleScript/pageitems:
+AddRemoveArticleMember.applescript
+CreateArticle.applescript
+RemoveArticle.applescript
+ReorderArticleMembers.applescript
+ReorderArticles.applescript
./scripting/indesign/scriptingguide/scripts/AppleScript/text:
+CreateLinkedStories.applescript
./scripting/indesign/scriptingguide/scripts/JavaScript/documents:
+ExportEPub.jsx
+ExportEPubWithOptions.jsx
./scripting/indesign/scriptingguide/scripts/JavaScript/pageitems:
+AddRemoveArticleMemeber.jsx
+CreateArticle.jsx
+RemoveArticle.jsx
+ReorderArticleMembers.jsx
+ReorderArticles.jsx
./scripting/indesign/scriptingguide/scripts/JavaScript/text:
+CreateLinkedStories.jsx
We lost the components that are were rewritten from JavaScript to C++:
./source/public/components:
-epubexport
-xhtmlexport
And we gained a whole bunch of header files for bosses associated with CS5.5 features, and similar:
./source/open/includes/ui:
+GroupButtonPanelEH.h
+MCntlMgrDropDownListEH.h
+MControlEventHandler.h
+PlatformDropDownListEH.h
+WDropDownListEH.h
./source/open/interfaces/layout:
+IArticleUtils.h
./source/public/includes:
+OdinBuildNumber.h
+sharedcontent
-IScriptUtils2.h
+IPDFDPartHierarchy.h
+IPDFDPartMetadataUtils.h
+IPDFStructureOrderPref.h
+IPDFStructureOrderPrefFacade.h
./source/public/interfaces/layout:
+ArticleID.h
+ArticlePanelID.h
+IArticleChildList.h
+IArticleFacade.h
+IArticleList.h
+IArticleMemberList.h
+IExportOptionsUtils.h
+IObjectExportOptions.h
+IObjectExportOptionsData.h
+IObjectExportOptionsSuite.h
+./source/public/interfaces/sharedcontent:
+ILinkedStoryPlacePrefs.h
+ILinkedStoryPlacePrefsData.h
+ISharedContentFacade.h
+ISharedContentSuite.h
+SharedContentID.h
+SharedContentUIID.h
./source/public/interfaces/tables:
+IExportTagValues.h
./source/public/interfaces/xmedia:
+EBookExportID.h
+IEBookExport.h
+IXHTMLExport.h
+pdfvt
+pdfvtui
+SnpExportEPub.cpp
+SnpManipulateArticles.cpp
And we gained a some sdksamples for working with PDF/VT:
+./source/sdksamples/pdfvt:
+DataSourceData.cpp
+IDataSourceData.h
+PDFVT.fr
+PDFVT.rc
+PDFVTExportProvider.cpp
+PDFVTFactoryList.h
+PDFVTID.cpp
+PDFVTID.h
+PDFVTNoStrip.cpp
+PDFVTUtils.cpp
+PDFVTUtils.h
+PDFVT_enUS.fr
+PDFVT_jaJP.fr
+TriggerResourceDeps.cpp
+WritePDFVTDataSourceInfoCmd.cpp
+
+./source/sdksamples/pdfvtui:
+DropDownListSelection.cpp
+IDropDownListSelection.h
+PDFVTUI.fr
+PDFVTUI.rc
+PDFVTUIActionComponent.cpp
+PDFVTUIDialogController.cpp
+PDFVTUIDialogObserver.cpp
+PDFVTUIFactoryList.h
+PDFVTUIID.cpp
+PDFVTUIID.h
+PDFVTUINoStrip.cpp
+PDFVTUI_enUS.fr
+PDFVTUI_jaJP.fr
+TriggerResourceDeps.cpp
+datasource.txt
That's about it. A bunch of internal resources in the build frameworks changed, some filenames changed to CS5.5 versions and versionless things, a few PNGs were added:
./external:
+PL_Articles_N.png
+PL_Articles_R.png
+PL_Overlay_N.png
+PL_Overlay_R.png
Blah.