Question to anyone: do you think of socialism as a political system, or as an ideology? There's a subtle rather than pedantic difference there. It's relatively easy to point to individual political ideas and label them "socialist" or "socialistic", but much much harder to describe any particular (existing) political system as socialist, because there'll always be someone who'll argue that it isn't.
The fact is, the Left has developed in many directions since the time of Marx, and while all left-wing thinking is to some extent derived from Marx (the only possible exceptions I can think of are certain religious groups whose positions on some issues are left-wing by accident more than design), not all left-wing thinkers are Marxists. Also, the Left is anything but monolithic in its thinking; it's always been a mass of in-fighting factions. So there are numerous ways of running a country that can be described as "socialist", in as much as they adhere to basic tenets of socialist ideology, but as soon as you try to define socialism as a specific political system, you're onto a loser.
Your old-fashioned lefties (on this side of the Atlantic) would describe China as state capitalist, and North Korea as a deformed workers' state. None would describe either country as "socialist". A certain section of the far left used to consider Soviet Russia socialist, as advertised; Trotskyists (the bulk of the far left from the 60s to the 80s) would have denied this quite vehemently. Trotskyists - though there are very few left - would also snort at the idea of the British Labour Party being socialist, even back in the 1940s, but for most Brits who identify as socialists, that Attlee government is in fact a near-perfect illustration of what they mean by socialism. Objectively, the best description of Attlee's Labour Party is "democratic socialist"; this is subtly but substantially different from "social democratic", a more common modern European form of government which would be (and is) dismissed as centre-right by the hard Left, but seems almost unthinkably left-wing to many Americans. To Europeans, social democracy is considered left of centre, but (apart from among a right-wing fringe) it's not considered to be socialism, more what Americans would call "very liberal".
Disagreement over what exactly constitutes socialism has long been a characteristic of socialists (of all stripes), so it's hardly surprising that the Right finds it so easy to pick up the word and chuck it around as they please. But no one who is a.) honest, and b.) in their right mind would describe Obama's America - or Obama himself - as "socialist". They might describe individual Obama policies as socialist, in a rather vague sense of the word, though in truth they're more representative of social democratic thought. Obama is a centrist, some of whose policies are centre-left, while others (e.g. de facto acceptance of the Bush doctrine) are clearly right-wing. He's not a socialist. That's about as close to clarity as we're likely to get here, I fear. Seriously, this thread could go on for 300 pages. It's impossible to come up with an effective definition of "socialism", with reference to an actual, functioning political system, because even socialists can't agree. What causes the confusion is not so much that the meaning of words evolves over time, more than left-wing thought has evolved over the last 100+ years, in twenty directions at once, with "socialism" (or variants) used as an umbrella term. It's like trying to get neocons, paleocons, Ayn Rand objectivists, Lincoln Republicans and Nazis under one roof, and agree on what constitutes "non-socialism". It's all a bit... messy.