Ferinex brings up a good point, but i might try to refine the discussion a bit.
Some nebulous ideas of communitarian controlled economies had been around in europe for a long while before the "Manifesto" came out. (cf. Fourier, Comte, etc., i don't know why i can only think of french socialists right now...). The question of if these types of socialist "governments" must necessarily be totalitarian is a sticky one, since A) there's so many of them, and B) most of them are very poorly defined anyway. Let's leave that one for the historians/poli.sci.s to figure out.
What the Soviets and Maoist Chinese attempted to do was capital-C Communism, as defined by Marx and Engels. Communism properly understood rests on an underpinning of Class Revolution and a complete subsumption of the individual into the state, not just "spreading the wealth", as some would call it. Whether Leninism or Maosim, like jorb said, it's all just about which cult of personality leads the armies and "police" at the time. So it is impossible for a state to be both legitimately Communist and non-totalitarian, whatever window dressing of words and gestures they implement.
The relatively liberal "socialist democracies" Ferinex refers to are an entirely different animal, something that I would personally not even call socialist (even though they would). Perhaps just distributionist, or mildly collectivist, but certainly not fully "socialist" in my opinion. It is THESE types of nations that can still be said to retain some degree of liberty. However, I think the way Jorb looks at is (as do I, and the entire austrian school) is that individual liberty and collectivism (socialism, redistributionism, whatever you want to call it) are diametrically opposed. At bottom, to the degree the state commands you by force how to dispose of resources you have created or earned by your own work and energies, in whatever way, then you are no longer free to that same degree. THAT is where the logical underpinning of jorb's argument lies. The point is not so much that 1) Soviets were bad, 2) Soviets were socialist => 3) Socialism is bad. More like:
* Socialism (in any form) requires governmental control of an individual's resources to be anything other than empty sloganeering.
* An individual loses liberty (by definition) in such a case.
=> Socialism, by definition, requires the loss of individual liberty.
We can leave the words "autarchy" and "despotism" out of it quite easily, although in the end that is where the slippery slope must inevitably lead. It is not a question of any past, present or future socialist regimes in actual existence, but the fundamental purpose of socialism. If you think the loss of individual liberty is bad, then you must inevitably be anti-socialist.
The socialist/collectivist reply to this is that no man in a post-industrial economy can produce much of anything without the help and assistance of his fellow laborers, and therefore owes all he has or produces to the "people" (which for Trotskyites and full-blown communsists resolves into the state itself), and individual liberty be damned.
[I won't touch upon the whole "real, pure socialism has never been tried" canard. No good can come of that.]
tl;dr version: Modern "socialism", in the form of Sweden or old-guard Canada, need not be totalitarian, of course. I would not call these countries properly socialist, however. In short, the degree to which a command economy exists precisely determines the degree to which those people have lost economic liberty, regardless of what labels you throw at it.
I recommend reading Isaiah Berlin on this topic. (note the sig

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*****
On a completely different track: What would you say the difference b/w autocracy and totalitarianism is?
"Bein' a minotaur is a lot like bein' a regular human except moo" - J. Rowland