It will take longer to carb and add a tiny amount of malt sweetness. Some people also swear that it creates smaller CO2 bubbles, but I'm not sure I believe that.
DME cost a little more, and it's a real pain to use if it is humid. Those are the only differences I can think of. The 5 oz that are added compared several pounds that make up the beer is negligible. I've got a post coming up on my blog in a few weeks that details the easiest way I have found to do priming sugar.
I've used both extensively and have seen no noticeable difference between the two. The sugar is dirt cheap and the malt is more expensive and a little less user friendly. I have not noticed larger bubbles using sugar.
The difference is that the brew store makes more money when you buy the DME and then you get pissed trying to work with DME when it gets stuck to everything.
I use LDM to comply with the German Beer Purity Law. Dissolve the required amount of LDM in water is the best way I have found, and then bulk prime or use a pump bottle (as I do). I work on about 8 grams per litre of beer, depending on style. And yes, you usually finish with very fine beading (bubbles).