ACORN did help out in Obama's campaign

But only for a few weeks.

http://www.pittsburghlive.com/x/pittsburghtrib/news/election/s_584284.html

Citizens Services Inc. was given about $832,000 for a couple weeks of campaign work in February and March of 2008. CSI has its headquarters at the same address as ACORN's National headquarters in Louisiana. This article says that Obama's campaign amended a federal reoprt on what CSI did for them, but that is not uncommon.

So ACORN, among probably thousands of other organizations, did some legwork for Obama's campaign in 5 different cities. They got $800,000 for it. It's not a huge connection, but its there.