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
fileindexing
foxit
home premium
ifilter
indexingindexing service
pdf
search
text
troubleshooting
wds4
windows 7
windows vista
x64