'as' and 'like'
The issue is whether or not ``like'' can be used as a conjunction.
The grammar nazi will claim that ``like'' is to be used as a preposition and ``as'' is to be used as a conjunction. Thus:
``Spanish is like Portuguese.''
but
``Spanish is as Portuguese is.''
The difference being that in the second sentence, ``as'' is being used as a conjunction combining the indewpendent clauses ``Spanish is'' and ``Portuguese is''. In the first sentence, ``like'' is used as a preposition, the same construct as ``Spanish is near Portuguese,'' or ``Spanish is around Portuguese.'' (Note that even though those examples are gramatically correct, they don't make a lot of sense. Cf. ``Colorless green ideas sleep furiously.'')
I think that this is an arbitrary rule that someone came up with a couple of hundred years ago and it got passed on for no good reason. Supposedly, their use has been documented both ways as far back as the 14th century, which is easily at the beginning of modern English. Use whichever sounds better. I doubt you'll find any dictionary that doesn't claim that both are both prepositions and conjunctions.