I've fixed quite a few bugs with Asunder, Hammer, and Paintbrush.

Asunder might run a bit faster, be sure Vsync is off and decrease you're render distance (data/settings.txt, turn renderDistance- down to 2 or 3) if you're still having problems.

I've also added a cylinder placement tool for Hammer! It's easy to make round houses like so:

*select two points on the ground a good bit away from each other, press the ~ key to open console*

Type in:

What that does is set's a cylinder of Grass, then sets a slightly thinner cylinder of air to hollow it out. That's just what I like doing with this tool anyway :)

the .setcylinder command (which can be shortened to .setcyl) works exactly like the .set command, you can designate two block type for replacing a certain block type with another and a percentage for percent fill. 

Once the tools are more developed I'm going to do a more extensive video tutorial to get some people started. Until then you can look at World Edit and Voxel Sniper tutorials on youtube, they function very similarly. You can also email me, PM me on the forums, or tweet me for more specific questions. 

-Hack

P.S. I have spring break after this week so expect great things to come from all that time off ;)