The most remarkable thing about Snow Leopard is simply that it can be installed on a Mac running Tiger. You do not need to pay the money to buy the boxed set to upgrade if you never upgraded to Leopard. This means that you can upgrade a Tiger computer to Leopard using this disk. It is up to the user to determine if they have an ethical problem with that; Apple certainly knew that this was possible when they released the software: they understand and use DRM effectively and always have. The fact it is missing here tells me that they are primarily concerned with getting Snow Leopard unto as many computers as possible as fast as possible. I am sure part of that is the desire to have Snow Leopard outperform Windows 7 which debuts in October. If you are updating from Leopard, Apple has continued to make it inexpensive for a family using more than one machine by pricing the upgrade at about $10.00 a machine (assuming you use all five). Not bad.So what do you get with Snow Leopard? The answer is largely performance boosts, although many of those are not really applicable (yet) since few (virtually none) third party applications use the performance gains offered by Snow Leopard. Similar to Windows 7s ability to load share between CPU and GPU, many of the changes in Snow Leopard will take several years for developers to really start to use and write programs for.Relying on 64-bit architecture through the entire OS, Snow Leopard is essentially an upgrade for the future: as developers write programs that take advantage of the new, higher ceiling, end users like you and I will benefit. For now, most of the performance increases are only applicable to Apple's own software. However, that's not to say these aren't nice or useful, and in some cases very impressive:1) Opening large photos is faster in preview mode2) Quicktime uses significantly less CPU on all Macs regardless of generation. Older Macs benefit the most with as much as 40% performance gains.3) Time Machine backups take about 20% less time4) Snow Leopard itself installs faster than Leopard5) Boot times are faster with Snow Leopard by 5-10%; Shut down times are slightly faster as well.6) File compression is also faster by 10-15%(These are somewhat simplified. If you want the exact numbers you can find them online: Google "Snow Leopard Performance")Of all of these, the performance increases afforded to older first generation Macbooks are the most significant. Breathing new life into older hardware isn't easy, especially not significant improvements. Snow Leopard manages to do just that and make even slower 1.6ghz MacBooks that much more useful.Installation itself is a SNAP (did I mention it takes less time than Leopard?). I've already upgraded a MacBook and MacBook Pro, and installation was simple, fast, and easy. I plan to install Snow Leopard on another older Macbook later in the week and will upgrade this review once I have.The few new visual tweaks are nice, but not the reason to upgrade. Better stacks is useful, as is the quickness of Finder, but overall I don't find myself blown away by the upgrade. This isn't an entirely new OS with a fantastic array of improvements, aside from the welcome and useful performance increases. That said, if you are a power user or just observant, you WILL NOTICE the speed increase, especially in Finder.*****UPDATE September 2nd 2009*****A few other changes of minor importance but sometimes great usefulness:1) Air Port now shows all available wireless networks and their relative signal strength, something Windows has done going back to XP, but that for some strange reason has been absent from OSX 10.X until now. Now when you turn on the Air Port you get a drop down to select which wireless signal you want as well as signal strength.2) The date has been added to the desktop. This isn't that amazing but it is useful.3) I am LOVING the way stacks work now. They're so much more intuitive to use and navigate, especially the ability to brows through directories directly from the stack itself.4) Trash has the ability to restore a file to it's original location right from the trash. This is a feature common to Windows that has been very strangely absent from Mac OS. It's nice to see them catch this omission and correct it, but very odd it took this long to do it.A MAJOR complaint:1) Seriously, no support for CS3? Why Apple, why? I don't have the grand to drop on the newest version of CS. This is very, very frustrating, and makes me wish I could take back a star and downgrade this to a 4-star review. CS3 is still so widely used that I'm amazed Apple decided not to offer support for it. If you want to continue to receive support for CS3 or don't have the money to upgrade to CS4, this could be a big deal and even a reason not to upgrade.A Minor complaint:1) One of my time machine back-ups for a co-workers Mac was seemingly corrupted by the upgrade. Fortunately they didn't have any old data they needed from that backup so I just made a new one with Snow Leopard that mounts just fine, but this is something to be aware of. If you have a critical time machine backup that you cannot afford to lose, I'd suggest making a backup of the entire drive (clone it) using SuperDuper! or something like it.*****End of update*****Snow Leopard will grow in usefulness as time passes. As I said earlier, once third party applications start to be written to take advantage of advancements in the OS, the performance overhead will become more and more useful. Expect to wait 6-12 months for that to happen, but in the mean time at least you're enjoying speedier OS performance for an very inexpensive price!