@Matthijs and Petri:
I have worked with Exchange since 4.0, MSMail before that and always in large corporate environments. Administration and support of PFs has always been a hassle. It is so hard to control culture and the fact many people see PFs as a file respository or extended file system. The current organization I work at has over 50,000 PFs. That is one folder for every .3 people. Some folders date back to 1997 and have the same content.
Removing content from an Enterprise organization that is involved in 100s of lawsuits a year creates a major issue. It took 3 years, but we finally have a suitable archiving solution. And no, we don't archive everything! People who do that are just as insane as those who want to keep PFs.
Besides the culture change for an organization, why can't PFs be replaced by Sharepoint or file servers?