Perhaps I am a bit optimistic in the power of Diplomacy. As a number of readers have pointed out to me, Mr. Obama has not changed a whole lot of US Foreign Policy. Pick a foreign policy situation, and Bush/McCain would have probably done whatever Obama's doing now (save perhaps Guantanamo, which is questionably foreign policy, and questionably changing at all). Obama's "humble" Diplomacy has many in the GOP grumbling, but it's really a great way to get everyone to like you without actually having to do any work.
Anyway. A few elections have come and gone, with some pretty pro-American results. Not every election puts most of its weight behind an American referendum, but US & Allied policy has been a pretty hot topic as of late. The EU elected pro-market, pro-US centre-right parties to its parliament despite rough economics and formerly-shaky US-EU relations. More importantly, Lebanon's pro-Western coalition held on despite a concerted and blistering push by a pro-Iranian (Hezbollah-led) coalition to get a majority in parliament. Many analysts are venturing that President Obama's speech on Islam may have made a difference, and indeed it may have. And, as soon as the speech was over, many political leaders said that they wanted action beyond the words, but in any democracy, words can go a long way in a voting population.
Mr. Obama's speech to the Muslim world was timed in particular to be right before the Lebanese and Iranian elections--two of the most important elections in the Middle East in the next few years. Even Iran's opposition may have gotten a bit of a boost (albeit perhaps futile) from Obama's speech.
Ultimately, it is easier to find a way to get along with an adverasary than to fight them. Particularly, when the adversary is the US and its Allies, finding some common ground and a leader that will reach out to them often reduces difficulty on your own part. Such was the basis of the "thaw" in the US-Soviet Cold War. Such may be the basis of a changing attitude toward the US in the Middle East in in the EU--if the US appears more willing to talk and work together, then the EU and Middle East will gladly accept the stance and jump at the opportunity.
Such speeches and diplomatic blitzes may prove very useful to the US, and are likely to prevent the "marginalization" of US power so quickly predicted by US and foreign pundits alike. Mr. Obama is taking a page from Sarkozy's diplomatic book, and may already be turning key results in favor of the US' long-term foreign policy goals.