(ISF) Move from PC to Mac?

Management has me researching the possibility of moving our office from PCs to Macs and I wanted to get the opinions, observations, comments etc. of the group. I believe they are interested in doing this mostly from a security standpoint. My concerns so far are cost, training, lost productivity, and the small market share Macs have. I know the debate of Macs vs. PCs is all over the map but am looking for a non-PC/non-Mac biased opinion.

I know this is a broad question but any information would be greatly appreciated.

Thank you,

Jeff Kennedy