Picroma Plasma seems like a really useful tool ... but my personal requirements are for a tool that matches my simple pen and paper sketching behaviour. I just want to produce simple sketch art, nothing fancy.
I may be wrong but Picroma Plasma, and a lot of vector applications, seem to involve creating 'guide lines', then tugging at handles, etc.
To me, this is not like sketching with a pen and paper.
I think there is a gap in the market for this type of simple application, just as there was a gap for wireframing applications a few years ago. In the meantime, SVG editor looks decent.