OS X is a superior alternative to Windows 2000/XP (certainly in the technical sense). The GUI is more different than incredible, but it is very polished and clearly targeted for the end user. It is easy to use, usually clear, drag 'n drop friendly, and smooth. First party (bundled) and "killer" applications are of similar quality. There are countless little things that make the experience almost like being served by your computer. On Linux, for example, its really the other way around.
The OS is far more configurable than Windows. It can basically be rebuilt, though these factors are rarely exploited. Also, security is not a problem. No viruses, effectively, and real permissions keep programs in check.
The current hardware is the best part. Apple has a reputation for standard quality in parts and stability in configuration. Mac's last a long time as well. But the current models are fairly exceptional. The G5 is a superior processor to the Intel and AMD offerings. The dual CPU configuration is an excellent buy price/performance, even when it first came out. The I/O is at the level of server components.
You can buy Mac hardware without OS X as well. For instance Yellow Dog Linux sells packages.
Finally, the cinema displays haven't really been bested. They are cheaper or the same price as equivalent products from other vendors and their quality is starkly obvious. You can also use one with an IBM-PC if you choose - there's a $100 conversion piece and you need a recent graphics card (or a model which ships with Macs).
Yes, I would say switching to a Mac is worth the price and transition.