TBH, most post processing is done in Photoshop CS2/CS3 which is available on both platforms. Again, Lightroom vs. Aperture .... who cares, they are both great packages in their own right.
OS, well that again is down to personal preference. Its really easy to get on the whole "hate Vista" bandwagon, even I did, until I gave it a try and really admit now its pretty cool. I remember when OSX first came out ... serious hatred for it; remember all the backward compatibility issues with software; as an engineer we were cursing it.
Hardware, well I have a solid Vista machine and a secondary XP platform that both work a treat. Coupled with a sexy looking Silverstone case setup and also an aluminium Shuttle with a gorgeous Sony TFT. I do think the imacs look really nice, although I do not think the big tower is a piece of art, preferably want to stick it in a cupboard as its just an aluminium box which takes up loads of space.
As for crashing, total nonsense one crashes more than the other. Its all down to configuration. I have had several OSX machines that have caused endless problems, the same as XP/Vista machines in several workplaces I have worked at. Although, PC support is much easier to find! My machines at home very rarely crash or cause me problems.
All down to personal preference. Gone are the days that one is better than the other!