Dilemma: To praise or not to praise?

As a preface, Dan told me that people with kids would appreciate all of this talk about bowel movements, but everyone else would think we were crazy. So, would I tell this to my brother James or sister Emily? James . . . Yes, but he wouldn't like it. Emily . . . definately. So now that you know what this blog is about feel free to read or not to read at your own wish being full aware what I'm going to discuss.
A few months ago we decided it would be really nice to have Vinson potty trained before the baby came. Well the baby is about two weeks away and we're still working on it. During the process we've had some dilemmas. From everything I've read (and I usually don't read anything about raising kids, but after a month of complete failure and starting to go crazy from it I figured advice couldn't hurt) this is a difficult process for the child to so to make it easier you shouldn't punish mistakes. I understand this. You should also praise good behavior. Duh. Often the only way to get Vinson to sit on the potty is with the prospect in mind that if he actually "performs" or as Dan would say, "makes a deposit" he will get some candy. But we've had a few circumstances where there's a question of how to react. I'll give the two most dramatic examples we've had and you'll see what I mean. Hopefully Vinson won't get too upset that these instances were made public :)
1. This was towards the beginning of potty training where we were excited when he knew he needed to go potty before actually going. I asked Vinson if he needed to go potty. "No . . . no potty, I don't want it!" You know, the normal reaction. Milliseconds later he pulled his pants down and aimed AT THE WALL and went potty. Do I scold him for purposely peeing on the wall? Praise him for knowing he had to go potty before doing so? I took the middle ground and tried not to react.
2. This one just happened two days ago. Vinson was sitting on the potty and shouted, "poop!" Yeah! Great! If I had to choose which mess to clean up it would be pee anyday. Well, he was curious and caught his poop, then was grossed out by the texture and threw it on the floor. SO CLOSE!! I ask you honestly, to praise or not to praise? I ended up doing a mixture of scolding and praising but he didn't get candy for it.