For those of you that use linux as a complete OS or those like me that have a duel boot with Windows 7 & Linux Mint 11 should really give Krita 2.4 a try.
It literally has an Alchemy brush engine and a mirror/pull function just like alchemy.
It has a Painter style engine allowing color blending and mixing and papers/textures.
It has Photoshop like functions allowing image stamps and custom brushes.
It has a Mypaint style procedural brush engine allowing for brush texture experimentation.
It has a Harmony style brush engine, with those cool soft webbed drawing lines.
It has vector - pretty much everything (brushes, text, art)
Basically this program kicks ass. There are a few bugs, the only one I found so far is the share brush function (allowing users to share brushes among themselves) is not working at the moment, but everything else I've tried has worked nicely. A windows version is supposed to be coming soon, hopefully by the end of the year which is soon. Check out the review by David Revoy: Cool article about Krita
and more info about the program and known issues here