Wee, got the PCI Hotplug core code and Compaq PCI Hotplug driver into the -ac kernel tree.
The PCI Hotplug core is one of the first drivers to be a filesystem. It uses a ram based file system to interace with userspace, instead of the ugly /proc or /dev nodes with ioctls and such. Just mount the pcihpfs file system where ever you want and you get a tree that looks something like:

.
|-- 2
|   |-- adapter
|   |-- attention
|   |-- latch
|   |-- power
|   `-- test
|-- 3
|   |-- adapter
|   |-- attention
|   |-- latch
|   |-- power
|   `-- test
|-- 4
|   |-- adapter
|   |-- attention
|   |-- latch
|   |-- power
|   `-- test
|-- 5
|   |-- adapter
|   |-- attention
|   |-- latch
|   |-- power
|   `-- test
`-- 6
    |-- adapter
    |-- attention
    |-- latch
    |-- power
    `-- test

Then just read the status of the different slots, and change the values by using 'echo' and 'bash'. So to turn on slot 6, you would do:

     echo 1 > ./6/power

The PCI Hotplug core also is the first chunk of kernel code that uses the EXPORT_SYMBOL_GPL() macro instead of the traditional EXPORT_SYMBOL() one. People at Intel are going to love that one :)