So far my experiences with the Mac have been mostly positive.
Graphically, I’ve never used a system that seems so fluid and, almost, physical in the way it is displayed. Things smoothly move around the place, message boxes emerge from the windows they belong to, staying firmly attached to their parents, and moving windows around feels far more solid — I guess this is all made possible by having properly composited and accelerated graphics so you can get the graphics card to do all the nice effects. Unless Vista is a huge step forward over Windows XP I don’t see this lead changing.
The system as a whole also seems cohesive and well crafted. Effort has been put into making things work as you would expect them to. The settings dialogs seem to be less over-whelming and more self-explanitory than I am used to, for example.
As I would expect for a system that has both software and hardware made by the same company, the integration and the it-just-works factor is high. An example I noticed early on came about when I tried to browse the web. I hadn’t plugged in the network cable, so Safari displayed an error message with some tips on what to do. I knew the cable was missing, so I plugged it in. The nice touch came when Safari detected the cable was plugged in and loaded the page I originally wished to view without my having to ask it to. A small thing, however, it makes the system feel more like it’s responding to your actions, as opposed to the feeling that you have to push and prod to make it do every small task.
The system goes to sleep and wakes up very quickly. Push the power button and a second later the machine is sleeping. Click the mouse and awake it becomes almost instantly — I’d imagine on a laptop quicker than you can lift the lid. The mac is very quiet while fully powered up, almost inaudible aside from a click of the hard disk every so often. When it is sleeping it is silent, I guess because every moving part is powered down at that point. It’s refreshing to see hardware and software working so well together. The power light even fades in and out while the machine is “sleeping” much like a sleeping person breathes slowly in and out.
The only problem I’ve come across so far is that my keyboard didn’t work correctly straight away — evidently the Apple UK keyboards are slightly different to PC keyboards. This meant some of the keys were more like the American-style keyboards. Fortunately someone has written a corrected keyboard map which is the work of a few moments to install and get working . I also installed a program  that remaps the ctrl key to the Apple “command” key so that ctrl-x/c/v and friends work as I’d expect them to. It also seems that the CD drive cannot be flashed to make it region free — if anyone has any advice on how to do that, I’d be very appreciative.
My final worry is that I don’t quite trust all the non-open data formats Apple uses all over the place, as Mark Pilgrim has recently been talking about. I’ve yet to come to a real decision about this, however, but it could be a reason to avoid the mac.