US$125 sounds like a bargain to me I think that's about the price of the sled in mine, before I bought the case and connectors.

I have one docking station already at work, but the temptation to acquire another for home could prove too tempting for me. And having made one, I'd find it harder to justify making another (novelty factor and all). I'd rather save myself day's work that it took for the first one even if it means spending more than I did on my parts (and it's almost certainly less).

Some observations, and (I hope constructive) criticisms:

• I put an ethernet socket on the back of mine (£5 or so) and I think that's the best connector option, as the user can then use the best length patch cord to plug it into the rest of the network. But if you leave space where I could install a socket myself, I'd be happy.
• I have a power-plug in mine to fool the player into AC mode, but I did think a bit about using mute or headlight sense to detect the sled. I considered wiring the input to the amp control, and checking for a transition when the display is activated, but your idea of strobing the serial sounds interesting. I like that.
• You don't mention what kind of serial connector will be exposed. I think serial is essential (for re-applying Hijack after an upgrade, if nothing else). I'd be willing to fit one myself, if you leave space for it.
• I suggest leaving some space to add extra audio connectors, for those who want rear outputs and AUX and MIC inputs. My dock has 3 pairs of RCAs (though I've only bothered wiring one pair).
• The size you mention sounds very compact - IWBNI there would be room to fit a tuner module (original or pca-kit) inside. My docking station is 11"x7¾"x3½" and some of the connectors were a bit of a squeeze. A bit more space would be useful for anyone customising their dock.

I've tried to keep my suggestions from increasing the cost - they're mostly places to leave space for keen people to add stuff.

All that said, I'd probably want one as a home-stereo dock with just power and audio-out, and use my existing dock for hacking.

Count me in for one.