Well, I tried to not answer this post but I couldn´t avoid it... hehehehhehehe... well, I use both painter and photoshop, I never used real oils or much of what is said that painter mimiks in real life, so I can´t say how good it is on that sense, I can say that I draw and paint doing stuff as an ilustrator... so I usually start drawing in painter and do the basic painting and blending, then I usually ended up moving to photoshop to finish the paint and wrapping it up... and it works for me... painter is really good to help with the drawing part of it, and photoshop is really good for the finishing stuff, like getting it all together and wrapping it up. Sooooooooooooo.... it all depends on what you do with what you have you know? Oh yeah I also use iluststudio when I have to deal with super perspectives ( like when I can´t get away with simple perspective)... anyhow I guess one can do everything with photoshop nowadays, but painter makes the drawing and inicial painting so much easier... so... in the end I´d tell you to get a trial and check it out, see if you like it and if it´s for you or not... and have fun.... I think archdruid got it right... 

well... have fun

vince

my blog: http://insanitariumenglish.blogspot.com.br/