[Igor Relja]

Thank you for taking the time to go through it Igor.  
I'm going to steal that intended audience bit as it sounds good.

Is there any car in particular you were wanting a line guide for?

Nah, just to try to make the whole process less painful in general. Like when I see a car I like, and I think that few accent lines would look good on it, how to "quickly" put them on.

For example, Superfast has that sexy line on the side. The best technique I could figure out so far is to draw it roughly by hand in Mudbox, export it to the Photoshop and fix up the edges. The problem is that UV lines are pretty jagged so I can't lasso them to get nice clean edges. Pen tool is a little bit better, so I make a path that matches UV lines, make a selection out of it, and fill it in new layer.

This is easy enough if the car doesn't have many panels or the UV is not too complicated (like M1, MX5, 812...), but in "bad" cases like P1 where you have to look at it for an hour to figure out which mask goes where... it becomes quite tiring quite fast 

I hope I'll have more time this week and I'll figure out more efficient workflow.