#1
This is something Ive struggled with for a while. It seems like something pretty popular in funky styles for example, that fast, sometimes 32nd note strumming.

http://www.youtube.com/watch?v=a9eNQZbjpJk

Guitar part that comes in at the beginning.

http://www.youtube.com/watch?v=Cqg_ZGcuybs

at about 1:05 (small example but it came to mind)

Any tips for getting that kind of technique? My pick has the habit of sliding right out of my finger at that speed, and my arm kind of goes into a stiff "raking" motion...
#2
He is just tremolo picking the b string and sliding. Get better alternate picking, and it'll be a breeze.
Michael Kelly Patriot limited
Michael Kelly Vex nv
PRS CE24

Tube Screamer
Zakk wylde od
Boosta Grande
Crybaby


Valve Jr
Peavey Windsor
Fender Blues Jr NOS
2x12 cab GBack

Bugera V22
Carvin Legacy

Vintage Rogers Drumset
Pearl ELX
#3
Well the first thing to always keep in mind is that you must always stay as loose and relaxed as possible (using just enough tension for the movements necessary to play what you want to play), especially keep the wrist. One way to explain the correct technique i've heard that has worked for me and others is that the motion is somewhat like how you'd shake your hand loose after slamming a door on it or burning your fingers. If you keep that sort of motion/looseness in mind, you can start getting the correct technique for strumming multiple strings quickly if you practice it enough, and eventually you'll be able to strum pretty quickly

also, it is always helpful to have a great guitar teacher who can show you the correct technique and go indepth explaining it and showing you exactly what they mean! I can only relay so much on a forum, unfortuneatly. Once you get the feeling for it down, it's all downhill from there