I have been building a pressure-sensitive digital painting system for a looong time. Currently I am working around a PowerBook 3400 and a CalComp drawing tablet (an "UltraSlate" Ooooooo!). Bulkier than an iPad or iPhone, but 512 levels of smooosh! Mac OS 9.1! Old school! You don't have to hold it in your hand!
I found the active matrix screen is useless in any level of daylight, so I built a baffle for it out of cardboard and velcro. I glued a tripod shoe to the bottom of the 3400 so that it can easily mount on a tripod, which is how I position my set up for plein air "painting". I decided also I would situate myself in Adobe Illustrator (rather than the more popular Photoshop) and paint in vector instead of bitmap...AI 10 introduced calligraphic pen strokes with transparency so I can build up a picture AND employ layers. Or not. I am trying to do something immediate and painterly that isn't "natural media"...I realize I have a LONG way to go here and must practice, but eventually I might get to a guachey kind of place.
This is an image looking out from the woods at a gravel road that leads to the dump. It's not a good painting, just a quick sketch, maybe an hour. It was about 40 degrees today, it felt really sublime to be out having an adventure, even if the outcome is not beautiful. I have painted here before, a little forest river - but today that water is frozen under our 34" of accumulated snow - I couldn't find it! After the painting is a view of the laptop and tripod (and my DEEP footprints).