Here is a shocking statement: I don't use Photoshop.
I haven't been able to justify the cost to myself, so I use a combination of Paint.Net and GIMP.
So far I have managed to make about $70 with my anthology which includes the comics. All but $2 of that has come from the Palm WebOS app I wrote. $2 is from Amazon Kindle. Not as easy to get the word out on that one. Palm is a small community, so I just hang out in the precentral.net forums and have a link in my signature. I'm averaging about 1 sale per day.
Since I have spent nothing thus far, I figure that is a profit of $70. If I bought the cheapest version of Photoshop I'd be in the hole several hundred bucks. I am nothing if not a capitalist pig... Oink, oink.
Honestly, the fact that my process is heavily traditional means that I don't have as much need for Photoshop. I also just enjoy the brush and ink.
Thanks for the comment on the iRobot comics. Tomorrow's comic starts a series of Star Wars themed ones. I'm releasing one per week right now on Mondays. I have a bunch of other projects going as well as my day job (which kept me working unexpectedly until 4:30 this morning...). I'm also working with my daughter to make some simple games that work in the browser and on WebOS phones. Hopefully we can get good enough with that to sell some games at $.99.