LISSPER  This app shows a lot of promise and the look of the pen is pretty nice. You can get some pretty stylized drawings. The stroke quality is okay, but I still see nickeling on fast, round strokes, which makes it limited. In this category, SketchBook Pro still gives the smoothest lines.  
(Version 1.3.5)

FROMAGE-HEAD  The really good point of this app is the ability to have speed and correct curves wich is really really important. A lot of apps have angular curves when you draw "too fast".

The pen feeling is quite right. But the absence of layers and transparency makes me prefer a piece of paper.  
(Version 1.3)

PLASTERPYRUS  If anybody gives creedence to any of the reviewes written here and you are a creative person that is looking for a really responsive drawing application on the computer and it desuades them from giving this application a test drive. Well you might just miss out! Given that this is a young application it is missing some features that I would love to see included, I say its off to a very good start.   
(Version 1.2)

HENRIKTEKNIK  Edit to my last comment:

It now works for me and it truly has the best drawing feeling of all apps I've tried so far.

Definitely keeping my eyes open for this app!  
(Version 0.9)

HENRIKTEKNIK  Would like to try this, but it unexpectedly crashes each and every time I try to start the application.

I'm using Powermac G5 dual 2.5 Ghz / OS X 10.4.11 / 1.5 GB RAM / ATI Radeon 9800 Pro XT (256 MB)  
(Version 0.8.1)

CROP  Lacks many features obviousely, but it's a pretty good starting point !

Just give it a try...  
(Version 0.6)

IRONINK  Looks like a promising little program. The lines I get have a great feel to them. If the program gets some basic tools -- full color picker, layers, tool panel, etc. -- by its full release it could be a nice program.  
(Version 0.5)

JCOHENSTUDIO  ArtRage is a fun toy, but it lacks the realistic feeling that TabletDraw provides. In particular, TabletDraw's relationship between pen speed an line thickness doesn't exist in ArtRage.  
(Version 0.3)

MACLOVER1.1  For $20 you get Art Rage...

http://www.macupdate.com/info.php/id/18357  
(Version 0.3)