I love the nav dock, though I had to seek out the special cable that gets you audio output through the USB port. I put the phone in the dock and its instantly connected to power and my AUX on my stereo. Cost me an extra 30 for the cable and a USB power plug but it was totally worth it. Here's a thread about it. http://forums.androidcentral.com/showthread.php?t=117395 .. or this one has a link to the cable http://forums.androidcentral.com/showthread.php?t=121237
I also have the simple desk dock which also has an audio jack, but I don't use that. Works fine as an alarm clock and sits there solidly while charging.
Woth it? It depends, The HD dock has a micro HDMI output, 3 usb ports, & a 3.5mm jack out & power input. You can hook up a wired keyboard & mouse to the dock, HDMI out to a tv, plug in your bionic & get webtop on the tv. I used this setup on a trip in a pinch to remote into work via logmein. You can also charge your phone.
You can use the mirror mode if you just want a big bionic screen, or view pictures & stuff like that.
I think there is a webtop adapter that is like $30 that will give you the webtop without the usb ports. (use a bluetooth KB & mouse)
If you just want to charge & have the bedtime/productivity mode the standard dock will handle that. (the HD dock will bring up those modes also)
It really depends on what you are looking to do with your bionic.
The HD dock and webtop adapter allow you to use the webtop feature of the phone over hdmi, where a straight hdmi connection will only give you mirror mode of the bionic screen. There was a webtop hack that could be sideloaded to enable webtop over just hdmi but I'm not sure if that's still working on the newer OTAs. Someone else may be able to answer that if you're interested.