The Campaign Finance Institute released its analysis of recent 527 and 501(c)(4) activity.  It’s a must-read, including the conclusion (although the groups themselves might not put it in these terms):

While soft money groups do not spend nationally on the scale of parties and candidates, they may spend enough on key races to help turn the balance in federal elections. In 2008, we are seeing strong early fundraising, changing practices among the 527s and the continued rise of a newer kind of 501(c)(4) actor. Some of these developments stem from earlier political controversies over 527s and the resulting regulatory response. Whatever perspective one takes on the rise of soft money groups in national elections, one thing is clear: it cannot help one’s understanding to look at each soft money group and its donors in isolation from others and from “hard money” groups and donors. They are, for better or worse, all part of a single campaign finance system.