Multumedia volume keys not working...

Ever since I messed around with sound to get Skype and my USB headset working, my multimedia keys on the front of my laptop hadn't been working. The on-screen graphic would appear but nothing I did actually effected playback volume, basically exactly as this page described it:

If after assigning as described above, your VolumeUp/VolumeDown/Mute keys seem to work (i.e. you see a popup window with a slider in the middle of the screen that reacts on those key presses), but the playback volume actually remains unchanged, you may also have to setup what mixer tracks (channels) these keys should be bound to. Refer to this section below.

So, following the advice in the section referred to I opened System/Preferences/Sound and on the Device Tab I found the selectino for Default Mixer Tracks. It was set to "Logitech USB Headset (Alsa mixer)", I changed it to "Capture: ALSA PCM on front:0 (Intel ICH6) via DMA (PluseAudio Mix..." and now all works well.