A few months back, circumstances forced us (my wife and I) to replace our sound system, VCR and TV, so I actually did follow all the back and forth about SACDs on the old BNBB before buying anything. To those of us who read any of his posts, Greg's "True Believer" attitude and brusque style of communicating could be kind of annoying, but he did seem to know quite a bit about the new format, and I learned quite a bit from following his posts.
From what I gathered, SACD is supposed to be able to break the blocky digital signal into such tiny parts that it approximates the smooth analog waveform, and thus the smooth, warm sound of analog, in way that conventional CDs can't, even 20 and 24 bit CDs. (This may not be an accurate description, and please don't ask me to explain why or how.)
There is also interest on the part of music companies because SACDs are encrypted in such way as to preclude burning exact digital copies. I don't even have a CD burner, but I'd like one, so this is one potential concern that I tried to learn about- apparently SACDs can be copied as analog but not digital. I do not understand how this works, or any potential difference in sound.
The way the "hybrid" discs are able to play on conventional players is that they have 2 layers- SACD and "regular" CD.
We ended up getting the Sony DVPNS 755 unit to use as a DVD player, and a Sony SCD C222ES 5 CD changer to use as our main CD player. If I were just upgrading a CD player, I'd look closely at the 755 or a similar unit- it plays video (but not audio) DVDs, SACDs and regular CDs. The 222 plays regular CDs and SACDs, but not DVDs. Since purchasing these units, I have stopped following the issue, but I'm pretty sure both have been superceded by newer models.
I remember Greg stating on a few occasions that Sony players had better "noise shaping" than Pioneer or Philips players, and sounded better. I don't really know what this means- something to do with how they handle the signal and noise reduction(?)
As far as sound, the few SACDs I have sound very good indeed. The new Rolling Stones SACDs are a truly amazing improvement over the old versions, even the regular CD layer, but this is probably partly due to the poor quality of the remasters they replaced.
I have not really gone whole hog into replacing titles I already have with SACDs, but I do buy them occasionally, if they have a conventional CD layer. My speakers aren't that great (the only part of our system we didn't replace) and I am not completely convinced that SACDs sound that much better than a really good digital K2 remaster, which are some of the best sounding discs I own. I will readily admit that the differences between SACD and Digital K2 might be more apparent if I had better speakers, and/or if I was a more discerning listener.
I do not own any single layer SACDs, and I won't buy any until I'm sure I can make decent sounding copies or "best of" discs for personal use. I don't like the idea of not being able to copy them, and the music industry controlling my personal use of something I paid for. If I want to make a "best of" disc to use in my car, I should be able to, especially at the prices for CDs. I also don't like the idea of possibly having a bunch of "white elephant" SACDs if the format fails to take off.