Interesting. That can be caused by a few different things: patched SDKs, locale issues and the cache.
Can you try this in a clean workspace just to see what happens?
1) File > Switch Workspace > Other...
2) Specify a new, empty folder
3) Create a new project and look for comments
If that doesn't work, you could try deleting and rebuilding your cache
1) Exit Flash Builder
2) Delete /Users/you/Documents/Adobe Flash Builder 4/.metadata/.plugins/com.adobe.flexbuilder.codemodel
3) Restart Flash Builder
Jason San Jose
Software Engineer, Flash Builder
Thank you Jason. Re-creating the Workspace fixed my issue.
I am having the same problem. I tried creating a new workspace, deleting the specified directory from existing workspaces, and no dice. I never get any information in the ASDoc tab. I didn't realize it was actually supposed to do anything to be honest!