24bit colour? 

I'm not sure about this one and will be checking it as soon as I'm back home and can examine some images on my desktop PC. Both LCD viewfinders show stepped gradations at the high end of the brightness scale. The light surrounding a bright bulb or the sun shows the very clearly. I would have expected 24bit colour to give a far better rendition of this area.

Now that I've had a chance to examine some files on my desktop computer, I've decided that the gradation is in fact 24 bit and smooth.  The stepping exhibited in the sunset image is the CCDs version of a shoulder in the density curve of photographic material.  Basically, it ran out of tones as it reached the limits of it's own capturing abilities.  You can call it a blocked highlight that has two or three steps in it rather than a single one as it might on a piece of film.

Audio - good and bad.

Sound is usually recorded nicely through the top-mounted stereo microphone and I've also had excellent results with a cheap mono lapel mic. You do have to keep your hands away from the area around the mic and this can be a problem if you are trying to use your left hand to operate the zoom slider... as can happen when you want to achieve a smooth startup.

There is one major problem with audio recording on this camera. The AGC (Auto Gain Control) cannot be turned off.  This is extremely irritating!
If you start recording in a silent or quiet location, the first thing you hear upon playback is the motor of the PC110 itself whining away for a second or two until the AGC slowly turns it down. Repeated short takes give your recording a saw-tooth amplitude of motor hum. 
Just as bad is the way it so very audibly increases and decreases as ambient noise comes and goes. It's really far too obvious for serious use and is the one thing that make the camera useless for recording your finally audio in real time.

I'm hoping there's a way out of this situation and I'll be trying to wire up a mic to the A/V input when I get back from my trip. I'd expect that port to bypass the AGC as it would make no sense otherwise.  If I had known that I could not disable AGC, I would not have purchased this camera. 

Noisy motor?

An update here is that I have found the motor noise not to be caused by the motor itself, but by the tape head as it spins across the surface of the tape.  When you remove the tape, the noise stops. Nice to know it isn't the motor, but that doesn't help with the noise.

Looking for specs on the web.

That brings up a point about the Sony web sites I browsed around trying to find information about the PC110 before I bought it. They all had virtually no specs beyond a basic feature list. There was no way to find out exactly what the camera could do and what it could not. 
The very poorly written manual (in English and Russian in this case) does let quite a few details slip out, but you have to know what to look for and then interpret the idiot-speak to get your answers.

I'm absolutely amazed that a massive corporation like Sony can't find someone who can speak and write English well enough to proof-read these manuals before they go ahead and print thousands of them to go into boxes with products that cost the consumer thousands of Dollars. (If you work for Sony and are reading this, tell the person responsible for these things to get in touch with me and I'll do it!) 

Anyhow, I ended up taking a punt and just ordered the 110 assuming that any problems with the earlier PC100 would have been fixed or otherwise dealt with. That holds true for many things, but this AGC issue is a real screw-up in my opinion.
I've since looked over the older PC100 model in more detail and can say that from the outside at least, the 110 makes the old model look a bit like a proto-type.