As much as I hate the comparison, there are similarities here to the WW1 buildup, in that a relatively minor squabble (and a civil war to boot) in a geographically sensitive area has the potential to draw in much greater powers (In this case, Israel and Iran, Russia and the US) as a result of alliances and local interests. Far and away the most dangerous development (IMO) is the Russia/Israel problem if both sides follow through on their threats/promises (The Russians to deliver the anti-aircraft missiles, the Israelis to stop them - shades of the Cuban missile crisis there, if on a smaller scale).
There are, of course, massive, massive differences between the world of today and the world in 1914 (or the world in October 62 for that matter), global interconnectedness being the big one, nukes being number two and a decreased element of societal militarization being number three. So I doubt that this could start anything like a 20th century style world war. But... the American position of treating Israel like a 51st state (while having no control over what they do) puts them in an incredibly uncomfortable position if anything serious starts to go down, especially in the event of a serious Russia/Israel row.
Iran is... well, not irrelevant, but not so much of a concern. They're betting 4 billion (or, realistically, a fraction of that) on Assad being able to cling to power. If he does, then they can claim to be a major factor in keeping him there, and probably keep large elements of Syria's elite very happy as well (depending on what exactly "the import of consumer goods" implies), while the US is betting that the rebels will win, and thus supplying them non lethal aid, basically for the same reason. That's not a major problem (unless you happen to be a Syrian civilian, but who cares about them in international gamesmanship) until one side or the other starts openly supplying weapons, at which point things start to change - psychologically if not practically.
Iran will matter much, much more is the Assad regime does fall - they perfected the art of covertly assisting and (probably) financing Shia militias to promote their own particular ideologies in Iraq. That's what they know, and that's bound to be their back-up plan in case the FSA wins, and get taken over by Sunni islamists (which seems to happen a lot in these Arab revolutions). They'll be a massive pain in the arse for whoever inherits Syria one way or the other, but in the buildup... keep an eye on them, but it'll be the Israelis, the Russians, Hezbollah and, of course, the Americans who're driving things if this does blow right up.
