This post isn't so much a language rant as a guided tour through an occasionally confusing aspect of English. The topic is what prepositions to place after the adjective different.
1. different from
[Basic form: X is different from Y.]
Use from if the next words are a noun, noun phrase, or relative clause functioning as a noun/object of a preposition.
Catholics are different from Protestants in terms of their history, theology, hermeneutics, liturgy, and polity.
As most cats note, cats are very different from dogs.
That result was different from what I had expected.
What you're doing now is different from what you'd promised to do last night.
2. different than
[Basic form: different than + clause without relative pronoun]
Use than if the locution following "different..." is merely a clause without any relative pronoun.
That result was different than I expected.
What you're doing now is different than you promised. (True, this sentence may be guilty of faulty parallelism. Just bear with me.)
3. different to
[Basic form: X is different to Y.]
Use different to only if you're British. In UK English, different to serves exactly the same function as the US different from.
British English is different to American English.
English and Scottish scones are different to American drop biscuits.
What you're seeing is different to what I'm seeing.
Mr. Maxwell's proposal is radically different to what you're proposing.