Today the FTC announced they had no problem with Google's acquisition of DoubleClick as proposed -- but there is a catch. If Google ever does anything to abuse their position in the online ad space, the FTC will act swiftly to diffuse the situation.
Because the evidence did not support the theories of potential competitive harm, there was no basis on which to seek to impose conditions on this merger. We want to be clear, however, that we will closely watch these markets and, should Google engage in unlawful tying or other anticompetitive conduct, the Commission intends to act quickly.” -- FTC press release
Today's majority vote (Pamela Jones Harbour voted against[pdf]) in favour of the acquisition is great news, but there is still the European Union that could rain on Google's parade. I don't know what the chances of it happening are, but if the EU denies approval, Google is out of luck. Their decision is expected before April 4th next year.