Microsoft
@Karsten: You can copy client permission to subfolders by right-clicking and selecting 'Manage Settings'.
@PaulVoller: You can deliver mail to sharepoint libraries from DL's, you should read the manual regarding mail enabled libraries its quite simple.
I would sum up the most common issue when moving away from PF's as 'user experience'.
Users, and many admins, refuse to accept change and dont want to navigate a sharepoint site because they have not taken the time to link outlook to their sharepoint data.
With the correct user training it is 100% feasible to get rid of PF's.
Spend the dev time/money porting exchange over to SQL instead of Jet and forget about PF's