When I first started looking at the activities of Burson Marsteller, the PR firm run by top Hillary Clinton adviser Mark Penn, I found a lot to dislike. Ezra has already mentioned the firm's union-busting services. Other unsavory clients include Philip Morris and Dow Chemical (for whom BM tried to shut down criticism of the Bhopal chemical disaster). But these events happened before Penn became CEO, so maybe it's not fair to tar him with their nicotine- and methyl isocyanate-tinged brush.
But here's some more recent information on Burson Marsteller: Even in the 2005-2006 election cycle, Mark Penn's company gave 57% of its campaign contributions to Republicans, and only 43% to Democrats. (You can see the list of recipients here.) Why is Hillary Clinton's top pollster running a PR firm that donates mostly to Republicans?