Well, let's get this thread going.
Really good question and since we haven't had a good controversial discussion in a while, let me throw in my 3cents.
I'm not sure the average smoker, including many competition cooks and judges and the public could tell a difference once the product is cooked.
However, I think, like wine and beer and other things that hit your taste buds, with a little experience and practice you can train yourself to pick them out.
I do think, in broad groupings, that woods have a different effect. Oaks, Hickory, Mesquite are pretty strong. Fruits; Apple, Cherry, Pecan are lighter. Now, having cooked a long as I have, I've trained my sense of smell and taste pretty well. That's also how I pick my wood. Do I want a strong or lighter smoke. For now, I'm using Pecan, probably 50% and Cherry/Apple for 50%.
Given the amount of smoke that gets into whatever you're smoking, I don't think, enough really adheres to give the average user enough sensory input to get enough flavor.
And of course our sense of smell makes the biggest input into this. We all start salivating as we smell the smoke from the smoker and that's what lingers with us -- and on us. But take your finished product out of the smoker, how does it smell to you?
And if you really want some fun. Try sitting at a table with 6 certified experienced judges and asking them to tell you what wood the item was cooked with. Needless to say, it's usually totally different answers.
Yes, I know, a lot of people will disagree.
Great, let the discussion begin.