The USPTO has revised its power of attorney and assignment practice effective June 25, 2004. The changes include:
1) Customer number practice must be used if more than ten practitioners are to be made of record.
2) Certain mail stops are being eliminated: CPA, Provisional Patent Application.
3) A new mail stop is being created: Licensing and Review ("L&R").
4) Only copies of assignment documents should be submitted. Submitted documents will not be returned or retained by the USPTO.
Link.