I just learned: In American English, it may be appropriate to use “different than” (instead of “different from”) if the words following it constitute a clause. Especially if (and this is the cool part) the clause is elliptical. So if you mean “Angelina and Jennifer are not the same person”, you would say “Angelina is different from Jennifer”. But if you mean that the way things are with Angelina is not the same as the way things were with Jennifer, you can say “Angelina is different than Jennifer”. (Source)
I love this about English — the subtle shades of meaning available to authors and speakers. I’m sure it’s true of all natural languages in varying degrees. I understand the lofty goals of linguistic prescriptivists (i.e., those who pass judgment on what uses, syntaxes, spellings, etc. are right and which are wrong) and authors of constructed languages (i.e., L. L. Zamenhof, the guy who came up with Esparanto (click here if you know of Esparanto and have a passing familiarity with the Eagles)). But I suspect that they lack appropriate reverence for the beauty of the tangled underbrush that they are so eager to clear.
I don’t think that I’m being elitist, really. I think you might could argue that I’m in favor of an aspect of English that makes it difficult for outsiders to learn and for native speakers to master, all because I have had the luxuries of time, money and access to education that allow me to appreciate it. But “different than” points up the problem with that argument. From my very brief reading this morning, it sounds like the prescriptivists had all but killed off “different than” as an acceptable use. I suspect that it did not end up in the American Heritage dictionary because it was revived by the literati, but because it persisted in everyday English. And it persisted in everyday English because people who don’t have MFAs found it useful.