If you have some time to try things out, there are a number of mind mapping apps, some of which are cross platform and free, that you might want to check out:
I just downloaded the (free) FreeMind, and it is pretty impressive, although so far, the moving of grouped objects doesn't give me as much control as Mind Manager (OS X).
Mind Manager (OS X) is pretty nice and quite intuitive, however even at the reduced price point (vs. Win), the amount of time I spend in mind mapping (not a lot) makes me consider the free apps. But I'll give them all a fair shot, and if worthwhile, would consider buying Mind Manager. It would be useful to know if MindJet has plans to get the OS X version up to par.