I find that none of the drawn emoticons I see ever really depict what I mean by :/ It's not a sad face as in that set. It's like "huh" or "what" or "ok", neither sad nor happy, it's puzzlement, filler, sometimes a "uhhh". Maybe that's just me though.
I think that conveys "bored" or "unimpressed" more than "puzzled". Funny how two dots and a line mean such subtly different things to different people.
I've been using "emoticons" for quite a long time (1980s) and to me :\ means basically what bellerocky described... you might be sad, or you might be happy, but basically you're just kind of confused.
In any case, there may be a generational component to this, or it might even be "regional", though the regions would be more about which forums, etc you hang out on rather than a geographical region.
Agreed. I have always read it as "meh" (closely related to "shrug" with asterisks), however I could agree with "what" as well. It's definitely not sad though.