Although i quite like the effect, i couldn't imagine much less professional than taking off one's shoe in the middle of a party or nightclub to reveal a wadded up playing card... bit gross. The closest i get is a pretty cool borrowed signed bill to sock. it's clean... the effect and the sock.
In my opinion, it is all about style and how you do the trick.
If you make it appear in your sneakers, I agree, this isn't very nice to do on a party.
But if you are dressed nicely and have nice shoes on and people see that your polite, there isn't any problem in my opinion.
Look at David Stone when he does his shoe productions, they are produced by a gentleman. It isn't disgusting like some people would think.
this is true, and very cool it is too, but every time i've seen stone do his shoe productions, he's always been behind a table, thus effectively hiding his feet. i think this takes the edge of what could be an interpersonal nightmare! plus, i was looking at the effect from my personal perspective, as a strolling performer, and i couldn't imagine myself doing it to be honest. i do agree with Dee though, i like the effect, and have done it a couple of times for friends, and it's a nice little trick.
Mac King, in his lecture notes (Mac King's First Lecture Notes - 1990) teaches a trick called "Mac King Meets Buster Brown", a non-folded card-to-shoe effect. Certainly, everyone knows whether they have the ability to do a trick like this without offending the audience's noses. Clothes are interesting though, and a selected card coming out of a performer's shoe can be interesting too. Also check out Paul Harris' Earth Shoes, from SuperMagic. I have seen good friend and awesome restaurant magician Dan Dygert perform this hundreds of times, and spectators nearly fall out of their seats when Dan dumps the huge rock from his shoes.
That's really interesting, every so often, i will start thinking about earth shoes again, and ponder doing it, start practicing, and even the practice sessions scare me off! Then i'll bury the idea, and a few months later, i'll remember earth shoes, ponder do... it goes on and on!
there is a huge chasm between the material i'd do for friends casually and the material i'd do at a gig, but i'd love to be brave enough to do earth shoes, generally! Give your friend a pat on the back for me, will you!