How Will Mac OS X Snow Leopard Upgrade Work?

OS X upgrades generally go extremely smoothly. You can imagine that most users will find it most convenient to upgrade rather than reformat, and Apple engineers work very hard to make sure the process is smooth. (You can rest easy that an upgrade install won't be missing anything you'd get from a clean install.) In fact, having upgraded to Snow Leopard on a few machines already, the install process is even more painless than ever before. With such a recent machine, I wouldn't foresee any problems.

It's always wise to check for compatibility of third-party software and devices — for example, my wife has a BodyBugg that depends on a kernel extension to interface with the system, and the driver hasn't been updated yet. For now, I'm keeping around a Leopard partition on the drive for the "just in case" scenario.

By the way, you can partition without formatting by using Applications → Disk Utility, and the migration assistant can transfer data between partitions. Thus, if you're paranoid, it might pay off to create a Snow Leopard partition, do a clean install there, and migrate your data from the Leopard partition. Once you know it all works, either upgrade the Leopard partition or stick with the new one, then erase and re-merge the unused partition.

With every upgrade of os x, I have found the OS upgrade has always installed smoothly and all. However, the issues I have seen have been 3rd party device drivers with major system upgrades. For example, I had an M-audio Firewire Solo interface quit working after upgrading once. I had to wait until M-Audio released a driver set compatible with the OS upgrade before I could get my recording interface to work. Some third party software can behave oddly from an upgrade also.

If you are running a stock mac system and pretty common major software, you should not have many hiccups upgrading. You might want to do a little research or wait to upgrade a bit if you have lots of non-apple devices and software. I normally wait to see what other people report having trouble with upgrading before I actually upgrade.