iSawThat, you can prevent spectators from concluding that a coin went up your sleeve by simply rolling up your sleeves before you perform the effect.

Re. the one coin routine I perform that gets a better reaction than anything else I do, it's a coin flight routine where I'm standing 10 feet away from an ungimmicked clear glass, I have 4 coins in my hand, one at a time 3 of the 4 coins vanish from my hand and audibly as well as visibly appear in the glass, I then wrap the 3 coins in a silk which I place in a spectator's hand, I stand back, the last coin (4th coin) vanishes from my hand and the silk jumps up in the spectator's hand while at the same time they hear the "clink" of the coin appearing, after which the spectator opens the silk and dumps out all 4 coins. Again, at the bottom line, I don't think that coin effects in general are any better or any worse than effects with other objects...it just depends on the particular effects you perform.

Could it be that magicians tend to be a little naive in what is deceptive and what not? And is there a difference in what is deceptive to laymen and to magicians...and what is deceptive for both?
I must say that almost 90 % of what I see in magic is not deceptive for me. Most of the time that is because of poor execution of the technique, but sometimes I also can see "thru" methods too easily...Now I realise I am a magician with a complete different viewpoint as layaudience. But I consider myself rather good at changing perspectives.
Constant listening to comments of spectators will open up a whole new world for you as a performer. It will teach you why they see something trivial as a major miracle...
Now the question you have to ask them is very simple: How do you think I just did that? Be prepared to be confronted with reality!

Because cardtricks are most of the time more complicated in method than cointricks (realise I say method, in no way am I suggesting that cardtricks are more difficult than cointricks, nor vice versa) a layperson will, of course have more difficulty in explaining the ins and outs of a cardtrick. Mess up a cointrick and you will hear the very hard truth: You kept it in your other hand...you have two...or even: those coins somehow "fit" together! Ugh!!!

Does this mean cointricks are less deceptive?
No! Except when done sloppy, you almost give away everything.

For those who say they seldom see a good cointrick I guess you've seldom seen an expert performance of coinstuff, or you are watching too rigidly from a magician's point of view.
I can vividly remember seeing Fred Kaps do a very simple Spellbound. Just 2 or 3 transformations...very basic. It looked incredibly magical in his hands even though I suspected how he did it (I was about 15 at that time).
Every time I am working on something I keep in mind: How would this have looked if Kaps did it?

I suggest you learn, no MASTER Shadowcoins and show it to a layman. Then ask him if he knows how you did it. Practice keeping your face straight as well, because they have absolutely no idea and will come up with the most outrageous solutions!

I agree that very good coinmagic is rarely seen...but that tells more about us as performers than coinmagic in general.
(And for me that counts in all of magic...)