(I am putting this in the eyeliner category because I find this pencil to work best as such, despite it being in the "Eye Shadow" section of the Urban Decay website)
I love this pencil. So. Much.
I have very oily skin, and I'm a bit of a klutz when it comes to eyeliner. Nearly every liner I've tried has, by the end of the day, migrated down and formed circles under my eyes, much to my frustration. To make matters worse, I find that most eye pencils are too hard (hurting my lid when I apply them and causing uneven application) or too soft (applying easily but migrating down almost immediately).
The 24/7 shadow pencils (I also own Delinquent) I've tried have been stellar, far better than anything else I've tried. They glide on easily and create a richly-pigmented line but stay put for 10+ hours without smudging or migrating.
Urban Decay also makes 24/7 eyeliner pencils (which, I *believe*, the shadow pencils are merely a thicker version of), but I find that the chubby shadow pencils are far easier for clumsy people like me :)
Barracuda is a nicely shimmery, highly-pigmented black. The shimmer is visible on the eye but isn't too jazzy or glittery for work.
These pencils are very expensive -- $20 a pop! But considering that nothing else I've tried produces anything like the results I've gotten with these pencils, I would gladly re-purchase.