Actually, the vast majority of the sentiment I've seen on gun boards (which has even been repeated on this forum more than once) is that Zimmerman was an idiot for getting out of his car, but that other than that we don't have enough information to either clear or convict.
As more information has come out, yes, the sentiment has shifted towards Zimmerman, mostly because the physical evidence that we've seen seems to support his statements.
That being said, don't know *still* means don't know. There's been a lot of supposition, a lot of inference, and a lot of discussion, but don't know really does still mean don't know.
I honestly think that what you're seeing as 'favorable sentiment towards Zimmerman' is a matter of perspective. If you know he's guilty, of course anything away from that view is going to seem favorable towards Zimmerman. If you are of the camp that says, 'let's wait for, you know, actual *evidence*' then the whole "Zimmerman is guilty, fry is arse" sentiment gets a little tiring, because we get tired of saying, "Hey, let's wait for actual EVIDENCE, and let an actual COURT, with an actual JUDGE, and maybe even an actual JURY reach an actual VERDICT.".