Nate,
Couple of things - do you currently use the billing/collections reporting in AC?
Second is know that rollback is not trivial, it requires either using a server restore point, or a complete OS re-install (per AC support).
If you go to 6.6.2, the positives are the letter-writer, and increased eRX functionality [when the pharmacy network is up].
I can give you more specifics if you sue the billing functionality.
