A few years ago I replaced the coil pack in my old Jetta in the parking lot of a Lowes at 5am in the middle of a crazy noreaster on my way to work. The intense rain caused it to finally go, I had to wait for Lowes to open to get the right socket wrench!
You can sometimes tell if they're about to go as you'll see some shorting and arcing through the gaps in the housing when you look at it in the dark.
I should probably pick one up for my A4, where did you guys get your packs?

 

Any good local parts store will have them, most of the aftermarket ones are OE coils in the box