The changes that matter, according to Newsweek, are 1) that donors' interests are shared immediately with their network of friends, 2) greater accountability and transparency, as Facebook Causes let you direct your donation quite specifically, and 3) the donors do the work, not the nonprofits.
All of these claims have been challenged. Discussions are raging on nonprofit tech listservs about the fact that anyone can set up anything as a cause, link to Guidestar, and off you go. Sometimes the "named cause" and the recipient organization don't match. Sometimes nonprofits have to set up FB causes to avoid having someone (maliciously inclined) do it "for" them - remember domain name squatters, now we have Facebook Cause squatters. And most point out that most of the causes have raised $0. See more here on Care2's blog and in this report on wired fundraising.