There's a MAJOR difference if you are doing it right! I'm sure there's a million ways to give a bj, but with an uncircumsized man, you have so many more options than just up/down, using tongue, using hands, etc. I personally find it way more fun, way more enjoyable, and a HUGE turn-on (maybe that's just me?)! Just the fact that they are more sensitive (the glans is usually covered by foreskin, so it's not in contact with much and doesn't rub against clothing all the time, desensitizing it!).
I've come into contact with guys that are so sensitive that you can apply no suction whatsoever during your bj because it's too much for them!
So anyway, maybe some tips you can use, too - Just use your imagination for the rest!
You can retract the foreskin with your hands and give a traditional bj, use your mouth to do it, pull the foreskin forward and work it back with the motion of the bj (with your hand or your mouth), you can slip your tongue between the foreskin and the glans, etc... maybe it's just ridiculously exciting to me, but I LOVE giving uncirc'd bjs!
On that note, DAMN! @#$%&@!!!! Why the hell am I not seeing the Scotsman til next Tuesday! ARGH!!!!