The new Mac OS X version 10.6, better known as Snow Leopard, is a sort of guerrilla update. It’s inexpensive and does virtually nothing to change the look and feel of your computer. In fact, most of its changes are under the bonnet – it uses several gigabytes less hard-drive space than its predecessor, and it should help your whole system run a bit faster.
While most existing programs will work just fine on Snow Leopard, a handful have experienced problems (at least in their current iterations). When you install Snow Leopard, your computer will automatically move these applications to a new folder called Incompatible Software.
Thankfully, Apple has published a list of known problem programs on its website (check under “Support”). So while you probably have nothing to worry about compatibility-wise, it’s a good idea to check this list before upgrading, just to make sure that nothing you rely on will be put out of commission.