The controls work passably well on my headphones. At least last time I checked.
One of my favorite capabilities with PA is the ability to migrate and hotplug audio.
I have USB headset (the USB audio is actually separate from the headphones, which is handy), Bluetooth headset, and onboard audio card. It's great to be able to just plug in my headphones and have it 'just work'. Also migrating audio from one device to another is fantastic.
For desktop audio Alsa/PA blows OSS out of the water. No question about it. Despite some of the ugliness.
As long as OSS exposes the timing information from the audio card back out to the applications then I don't see why OSS/PA wouldn't be any worse. Just as long as FreeBSD/Solaris/whatever has the ability to intercept applications trying to use OSS and pipe it back through PA transparently.