I read with interest a newspaper article this morning which described a growing practice among liberal Christian churches in Houston, of celebrating the Passover as well as Easter. It is celebrated with a Christian interpretation of the lamb, with Jesus' passion at its heart. Some of the local Jewish communities are concerned that their festival is being usurped by the Christians, stating that the Christians are taking their holiday and symbols and investing them with meanings foreign to them. They are not happy with this new Christian tradition. One rabbi said that he doesn't mind having other groups celebrate Passover as long as it is celebrated as Jews would do.
Being a historian of early Christian, my first reaction to this is well, what is new? This is the exact conversation (with the same complaints) that the early Christians and the early Jews were having in the first and second centuries. Most Christians in this period celebrated Passover as a Christian holiday altering all the symbols so that they pointed to Christ. Our earliest homily is by Melito and it is the homily he preached at Passover. It has this classic reinterpretation, which also ends up being very anti-semitic in its orientation as you might well imagine. Easter isn't mentioned in any documents as far as I know until the fourth century (Nicaea, 325). When it is mentioned by Socrates Scholasticus (380), it is recognized as a local custom that was not biblical (that is Jesus and his apostles didn't command it) but had developed in the catholic churches as a way to celebrate the resurrection.
UPDATE: Link to Melito's sermon