I'm going to be cautious in my response to the still somewhat vague commitment by the US to arm the Syrian rebels; the US commitment seems ambiguous at best. The evidence that the Syrian regime has used sarin is the ostensible reason for the change, but clearly the recent successes of the Syrian regime are also part of the calculation. But it's also clear the US is not diving in head first, but perhaps testing the water with a toe.
The Syrian regime's behavior is atrocious, but intervention without a clear understanding of what the US can actually do to change the outcome could be disastrous, especially as there seems to be no great reservoir of popular support for such a move. The Libyan model does not apply, since the factors of Iran, Hizbullah, and Russia were not in play in in Libya. The fact that the US Administration seems unenthusiastic but is responding to political pressure also may weaken any response.
I don't think the Libyan model applies. I worry that the Vietnam model does: a complicated geopolitical configuration that limits one's options and prevents an all-out commitment, combined with a lack of political support at home. Yet I know many people who know Syria far better than I do who are advocating doing more, and I also respect those views.