It is a real issue, but it depends both on your personal sensitivity to it, and the drawing app that you're using.
Specifically, many drawing apps primarily use the CPU, rather than the GPU to do the draw processing. You can see this in apps like ArtRage or Brushes, the more you've drawn on the canvas, and the more layers you've added, the more lag is introduced to the tracking of your finger. With the new iPad, this issue will be compounded for drawing apps that aren't GPU accelerated, because the CPU remains unchanged from the iPad 2, but the resolution has doubled.
Now, in my opinion, the gold standard for drawing apps, from a technical standpoint, is Procreate. It was built from the ground up around the GPU, and it is phenomenally lag-free. The new iPad has twice the GPU cores of the iPad 2, and the developers claim that the upcoming version update maintains awesome performance on the new iPad:
http://savage.si/blog/2012/03/16/the-new-ipad-procreate/
Some people will put up with a bit of lag because they prefer an app that might not be as performant, or maybe they're not sensitive enough to the lag and don't perceive it to be an issue. This is something you'll have to make your own judgement about as you try the different apps available.