I was using Vista x32 Home Premium, WDS4 and IFilter to index text content in 20,000 PDFs with no problems.
I just installed Windows 7 RC x64, which is supposed to have the WDS4 functionality built-in. I have swicthed on pdf content indexing in the Indexer control panel, enabled content...
adobe
configuration
content
directory access
file indexing
foxit
home premium
ifilter
indexing
indexing service
pdf
search
textcontent
troubleshooting
vista
wds4
windows 7
x64