That's the powerblock that does all the clever work for that. There are a couple of pins out for the switch - the actual switch itself, and the LED pins. (you can kind of see them in the photo below, although I have connectors plugged on to them)
When powering up the powerblock pulses the LED, then when it's on, it's steady, then on shutdown it pulses it (slower I think).
As it's just a couple of pins on the Powerblock, you can connect any LED to it - doesn't have to be the LED in the button, so I guess you could connect a whole bunch of LEDs to that and they would all pulse on startup, be steady on power on, and pulse again on shut-down.
I probably wouldn't try to run a Christmas tree off of those two pins, but if it's just a few additional LEDs it should be fine I would think.
Anything running of the normal rpi USB ports though (like my marquee light and couple of illuminated buttons) is just on all the time (when the rpi is powered on). Actually they flash a couple of times on boot up, I'm not sure why that is.
I've refined my LED power switch now, and upgraded to a chrome one. Also shortened the cabling and heat shrinked it as it was very messy.
I still have some spare ones (green plastic LED latching buttons) if you want one. I made a couple of shorter 20cm ones and also no longer need my old ridiculously long cable one (as seen in that video!). If you want one, drop me an email at GtB at GtBFilms dot co dot uk and I'll stick one in the post.
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