First I think Vista is pretty decent, I run it via Bootcamp and VMWare. I'm by no means anti Vista, though I do prefer Leopard and run it most of the time.
Second Time Machine is for Backup and as far as I understand it Shadow Copy is for version control. If you are doing version control you'll still want backups, if you are doing backups you might still want version control. Leopard ships with subversion pre-installed.
Third there is no double standard over Snow Leopard. Snow Leopard looks set to make far more ambitious architectural changes over Leopard than Vista did over XP. We will only know the truth once Apple delivers, but Grand Central and OpenCL could potentially offer very big leaps forward for performance. It's not a fan boy thing, people outside the Apple world are very interested to see what Apple delivers in these areas. Parallelism is a huge challenge.
As someone who has been in the I/T industry for 20 years.... I hope for God's sake that shadow copy is not implemented like shadow copy is on servers and such.... Time machine is a backup, which takes your entire hard drive and backs it up at a given point and time, which you can go back to.
Shadow copy (as one thinks of it, how it has been used for years) is a parallel running hard-drive where if changes are made on the original hard-drive they are copied (at about a 1 minute time delay) to a second hard drive.
the advantage of shadow copy:
1. if you main drive fails, you mount the shadow as your main drive, repair the broken drive and make that the shadow - thus you keep running with little down time and then all your work is applied to the new shadow when it becomes available.
2. You can dismount a shadow to make a backup and then remount. Users can still work during the dismount, backup, and remount.
3. Shadows usually re-sync with the main drive automatically.
The dis-advantage of shadow copy:
1. Undiagnosed problems that cause corruption (the kind where problems happen for days to months, but yet have no symptoms until the system crashes) get copied to the shadow as well, thus you end up with bad shadows and bad backups which can lead to restoring days or months of lost data (i know I been through this number of times).
2. You usually have to have some type of journaling turned on, and journals have to be applied in order to keep the data in sync. Something goes wrong with the main or shadow drive and the journal files end up filling up and cause the system to crash - or worse (if the journals are allowed to grow unrestricted) run the entire drive out of space. I have also seen where journal files get corrupted or applied out of order, now there is a real mess.
3. I have ran into issues where a shadow drive gets in a locked state and causes the entire system to freeze.
to me, Shadow can be a good thing - but if it works the same way as it does on servers; it will serve as little benefit to the average user. Reason, more confusion on how to recover in event of a problem, 2 people will rely on the shadow and not make backups - which can lead them down a bad road.
I have seen even with shadows and backups, sometimes a problem goes on for so long with out symptoms (not really, but I never worked in an I/T shop where people actually look at their event logs until a crash) - that the shadow and backups are bad, so you still have to load the original operating system; break out your application CD's and try to figure out how to recover data.
Good points and bad points - but I can see more people running to their local repair shop. Also with a shadow, depending on how implemented, you cannot just copy a file easily.
I prefer time machine and to back up my own data files regularly to a Cd-RW or other means.