[noggin]

My WDTV Live does 4:2:2 MPEG2 (which was a big surprise I found out by accident). I've seldom found any hardware outside the broadcast sphere that does 4:2:2 anything...

Is 4:2:2 noticeably good?

Yes - though this is probably more because most 4:2:2 content is broadcast quality source (or contribution circuit quality) material before the compression to broadcast or optical distribution bitrates. So it looks nicer not just because it is in 4:2:2 but because it is a very high quality source!

440Mbs 4:2:2 (as used on HD-Cam SR) looks very nice indeed (it uses MPEG-4 Part 2 Simple Studio Profile at 10 bits), as does uncompressed 4:2:2 as used between studio cameras and vision mixers (aka switchers). (SR decks can also, optionally record 4:4:4 - which is a format mainly used for camera acquisition and interchange during production at the very high end, and some can also record 2 x 4:2:2 feeds simultaneously for 3D acquisition onto a single deck)

4:2:2 MPEG2 was widely used as the broadcast satellite standard for SD and HD - with HD bitrates in the 38-60+Mbs, though H264 has now significantly taken over and is more widely used in the 18-40Mbs range for satellite (and compressed fibre) distribution. At these bitrates you do see some compression artefacts (as you do with Blu-ray) - but it still looks very nice indeed.

I'm not sure you'd tell 4:2:0 from 4:2:2 in most cases 'on screen' - but it does have benefits (particularly with interlaced content) in the production chain. If you are using 4:2:2 vs 4:2:0 sources for chroma-key, you do get better results with 4:2:2 - though this may be as much because 4:2:2 is usually a higher bitrate source than 4:2:0. 4:2:0 is used to subsample and reduce bitrates prior to compression to further reduce the final bitrate required and reduce the compression ratio required in the compressed codec. Hence SD DV25 is 4:2:0 (or 4:1:1 in some cases) whereas SD DV50 (and IMX 50) is 4:2:2. Back in the day news SNG links were c.8Mbs SD in 4:2:0 MPEG2 compared to 24Mbs HD in 4:2:2 MPEG2

Have you ever seen 4:4:4? If so, Do you see any difference between 4:4:4 and 4:2:2?

Yes - and before that I saw uncompressed analogue RGB camera outputs with equal bandwidths. You can see a difference if you are close to the screen and look very critically. The real benefit of 4:4:4 is that you get much better results when you colour grade in the edit, and you can also get higher quality compositing using green-screen (as you have full bandwidth across the capture, without having Cb and Cr colour difference signals subsampled)