See this collection of links for all the disgusting details. The Center for Competitive Politics has a summary analysis (and will send you a more detailed one). The text of the bill itself is online.
I'll summarize it like this: the Democrats of the House passed a bill that essentially “tweaks” the First Amendment in their favor –, by making it more difficult for anyone other than unions and certain favored lobbying groups to get their political messages out to the public. If it manages to pass the Senate, Obama has already publicly stated that he'd sign it. This would be just in time to make it harder for anyone other than the Democrats to get their message out in the upcoming November elections, which are guaranteed to be the most contentious in many decades.
The only good news in all this is that the consensus of legal pundits is that the bill doesn't stand a chance of winning a Supreme Court challenge (but of course, those take time and money).
Some assembly required.
Are you pissed off yet? Let's throw all these bums out come November!