I wouldn't, it's not that OSX is a bad operating system, I've just never got on with MacOS in any of it's incarnations, and it doesn't do anything additionally to Vista (and does a few things much worse) that I consider needed.
Couple that with the likelyhood of all the things that are currently considered to be better with OSX being largely based around a tightly restricted, closed enviroment rather than an open enviroment requiring lots of third party driver support, and the argument for me becomes moot.
In answer to the above post, in order for me to take time to install, learn and adapt to a different operating system, it would have to offer specific benefits, either in software or in general (for example, in employability) for me to undertake. I might install it if it was free, but even then I doubt it. (I've played with enough linux distros that are free and not been converted, mainly because if I want something that behaves like windows, I'll just use windows)