After Beta2 we have made some big changes to webconversion tool.Some of them are
Moved all extra class/structs/enums to App_Code folder, so that other files in the web can use them.
CodefileBaseClass support is added. If a page has CodeFileBaseClass attribute asp.net runtime will not create protected member variable for ids in the page if base class already declares it.
Fixed a code-behind/App_Code referencing a code-behind.
If code in the App_Code folder is referencing code behind tool creates an abstract base class in the App_Code folder.Public variable and static methods will be moved to the abstract base class. To suppress this DWORD value KCU\Software\Microsoft\VisualStudio\8.0\WebProjects\GenerateStubsDuringMigration can be set to 0.
If code-behind is accessing another code-behind a reference tag is added to the page. However this could cause circular references to avoid circular references abstract base class may be generated.
Excluded files. Conversion report will caution about files are being excluded from Everett Web project. After conversion users need to manually exclude these files from website. To do this select the file right click exclude from project.
Change in default backup location. If the solution file stays with within the website folder default backup is within the web, Backup folder staying in the web site folder causes build error. To avoid this default backup location is changed in this case.
HTML validation after conversion. Conversion tool changes teh HTML validation target to IE 6.0 to supress the validation errors. This can be changed at Tools->Options->Text Editor->HTML->Validation->target.
Changes in conversion report. Most of the harmless warnings changed to comments. So by looking at errors and warnings user should be able to identify what need to be fixed.
Common conversion issues are documented athttp://msdn.microsoft.com/asp.net/migration/upgrade/default.aspx
I will be updating blog with common issues users may run into and how to fix them, in a seperate blog. And I will be happy to answer any questions you may have in converting your web to whidbey.