Just got my 400 and didn't see any other post about it, so I guess that's what makes it official.
This is my first HD and Flash base CC, so right away notice the small size. I'm charging the battery at the moment, but while tethered tried a quick pan around the room and a few still shots. Full battery charge is 160 minutes.

First impressions:
I have pretty big hands, but the menu navigation was tolerable. Below the screen are 5 small buttons that you use in conjunction with the touch scroll bar on the left edge of the screen. My boys like that the scroll bar lights up blue and looks like a Stargate Atlantis door control panel. Zoom can be controlled by the scroll bar, but it is cumbersome compared to the rocker switch on top of the body.

Found that the small light next to the lens only activates for still shots.

The zoom control is quite handy and very smooth and speed progresive with pressure applied.

It looks like most on screen visual indicators are optional. Initially like the mic level meters overlaid on the video. Maybe that will get old.

I'll comment on the video after taping a marching band / football game tomorrow.

Forgot to mention that this $many CC doesn't come with a $2 mini HDMI cable. First view using component output was not impressive through my SR805. I'll try direct to the projector and again when I get the cable.

A little more time with the 400. Here is what I put on my Amazon review.

The usability is ok. The main user interface is around the display. The buttons along the bottom are a little small for me, and mis-hits happen and the touch sensitivity takes some getting used to. The other main input device is the touch sensitive slider along the left edge. This isn't bad but over shooting the intended selection happens about 30% of the time.
My initial play back review was on a 720P TV using a HDMI cable. I shot all the video on the highest quality setting (the CC calls it Blue ray quality). Some of my initial video was taken in lower light conditions and the graininess of the video was very noticeable and rather disappointing. Video taking in direct sunlight was very good.
My next viewing test was on a 1080P projector (at 10' screen size). The grainy playback on the 720P TV look noticeably better on the 1080P display. Good enough to change my mind on returning the CC.
The still shot capability is quite handy, the switch for full res still mode is well placed, and taking stills during video recording is very easy. I haven't taken much high speed video yet, but it looks like it will need a lot more light than normal recording to work well.
The unit is very small and light. The hand strap is too short, I had to go past the widen "safety" part of the strap, so there isn't much velcro grabbing.
I'm still on the first battery charge, so no data on how long it will last.
Overall I like the features and using the CC. But if my DV Sony hadn't broke, it wouldn't have bought this. The picture isn't that much better.
I've yet to use the included software. I'll add feedback on that later.