It seems that each time the IRS “improves” its Power of Attorney form (Form 2848) they make it more difficult for practitioners.  The latest revision is dated 3-2012.  Fortunately, forms submitted prior to the new form being issued are still acceptable.

First, you now need separate powers of attorney for husband and wife.
Second, in the area on the new form where you (the representative) list your name and other information, there is now a very small box.  You need to check this box if you want to also receive notices and communications from the IRS.  This box is new and easy to miss.
Third, review carefully whether or not you want any of the additional items listed in paragraph 5, acts authorized.  These involve the power of disclosure to third parties, the power to substitute or add representative(s) and the power to sign returns.  Many times, you will want the first two powers.
Fourth, make sure the size of the print you use when completing the form is large enough to read when the form is faxed.  The IRS will reject a POA that is legible to you when it becomes illegible when faxed.  This is the case when using the IRS.GOV fill-in on line Form 2848.
Fifth, despite the section for it on the form, you do not need to provide a telephone number for your client on the POA.  Leaving the box blank might reduce the amount of calls to your client by the IRS.
Sixth, to be safe try to keep the date of signing of the POA by the client within 3 days of your signing the POA as practitioner.  Otherwise, the IRS may reject the POA.  (Usually anything within a month is acceptable, yet sometimes they say three days – be safe!)