The rule for the U.S. is that the Friday penances are observed on all Fridays that do not fall on Solemnities. This week, March 23 - 29, 2008, is Easter Week, and each day is a Solemnity. That means that for this Friday, the 28th, we may omit the customary penance. The remaining Fridays until Pentecost Sunday on May 11 are simply Easter Weekdays, and the usual penances are observed.
Betsy