I needed to make a couple of long mitre joints for a back-drop panel.
So I marked pencil lines on both sides and opposite sides of the
panel.
I covered the lines with two layers of tape. The tape will act like a
hinge.

http://s123.photobucket.com/albums/o...wlinesTape.jpg

Then I took a 60-degree V-Bit and routed along the line, right down
to, but not through, the double layer of tape.
I took more than one pass. You can, of course, do this with 90-degree
bits as well.

http://s123.photobucket.com/albums/o...nt=VGroove.jpg

I then ran two small beads of adhesive along the length of the
grooves.

http://s123.photobucket.com/albums/o...lueandFold.jpg

I folded and held the fold in place with a few passes of hotmelt.

http://s123.photobucket.com/albums/o...=ClampMelt.jpg

When the glue dries, I will paint. A quick scuff of a sanding block
will make the mitre seam smooth enough to paint without having to fill
any gaps.

http://s123.photobucket.com/albums/o...hibitPanel.jpg