Unlike the previous version's 300 new features, Snow Leopard was introduced to the Mac community with zero new features, but loaded with welcome enhancements reducing the size of the OS and increasing speed for the user experience, including faster startup, shutdown, backups, and page renderings.
If Leopard represented a new path, Snow Leopard is a moving walkway in place of the sidewalk.Snow Leopard takes everything the community loved from 10.5 and makes it snappy.
Here's my two cents from the perspective of wiping my MacBook for a clean install of Snow Leopard:
In a word, compatibility.
Snow Leopard doesn't install Rosetta compatibility out of the box, so when you go to run an older program written to be PowerPC compatible, like Disk Inventory X, you are prompted to download Rosetta. It's a quick download, but a poor decision on Apple's part to eliminate it from the install.
The native Snow Leopard apps, like Safari, Mail, etc, are 64-bit and many/most of the plugins and enhancements in the wild simply aren't compatible (yet). Yes, this isn't a reflection of Snow Leopard, but it is a real-world issue for many users (or at least it is for me). Some of my most "essential" items simply don't work out of the box. Wisely, Snow Leopard will allow you to run Safari, for example, in 32-bit compatibility mode, but Mail gets no such "limbo mode" support. My list of busted haxies includes:
1Password Safari Plugin – upgrade coming, works in 32-bit compatibility mode
Keywurl Search Plugin for Safari – upgrade coming, works in 32-bit compatibility mode
Letterbox Mail Plugin – non-functional, upgrade "coming soon"
For more on compatibility, there's a Snow Leopard compatibility wiki for reference. The "good" news is that most compatibility issues can and will be resolved, but – as Tom Petty says – the wa-ai-ting is the hardest part.
There are some bugaboos in marrying the 32-bit support into the core system. For example, many of your custom menus in System Preferences are 32-bit. Since Snow Leopard initiates System Preferences in 64-bit, the system has to close & restart System Preferences if you want to access legacy menus. You can set System Preferences to only open in 32-bit mode as a work-around. Chalk this up to "tweener" stage compatibility, but… ugh.
All in all, the Snow Leopard upgrade was super easy for me. I'll detail it in a future post, but – suffice to say – the enhancements way outweigh a few compatibility issues on my plugins. And, since there are work arounds for almost every item, there's no reason not to upgrade.