Grrrrr, you vector people and your crisp, clean lines. It can show naught of the human condition!
(Just saying that Vector gives you that Virmir-like, smooth, computery look, but using raster((non-vector)) tools can give you a nice sort of look, too.)
Well really, you dont need vector to get Virmir's "look", he just used) a Round, Pressure sensitive, brush with no Opacity change (ie: when pressing harder with the pen, it only changes the diameter of the brush, not how dark it is). Its a basic Brush in many Digital Art programs, Photoshop, Corel Painter, OpenCanvas, etc etc, you could easily take any of these and get the same type of brush if you fiddled with it.
The vector stuff, really just makes it easy to resize the lines, + it has a 'Smoothing' effect on the lines too (its a setting that can be set, in SAI) Vir told me before he uses... 0 or 8 for sketches and I think 15 for Inking.
I think the real
'secret' to his style' is more of the fact he uses the tablet PC to draw his stuff, where in making a line he would naturally go from soft-hard-soft in pressure to get the Inked line look. You could emulate it through Photoshop or SAI but the whole process is 100x harder, where you would need to manually tweak each line to emulate the thickness differences.
Uhh, how do I go into "edit mode" anyway?
In SAI, and you've made a 'Linework Layer', right underneath the 'Pen' tool is the 'edit tool'. But To fiddle with a Vector lines thickness, use the 'Pressure tool' (which is the to the right of the edit tool) then the lines will start showing those green dots again, where you can drag them to make the vector line in that area, thicker or thinner.