I have a confession. I am a Mac guy. From the very early days of home computers I have pretty much always had a Mac, either at school/work, home or both. My lab is entirely Mac and I was never forced into using a PC throughout grad school or in my postdoc, since those labs ran Macs as well. I can use a PC with no problem, but the times I have owned them make me pine for my Mac. There really is no comparison, especially when you consider the rate of performance decline as the machines get older. You can run a Mac for years on end, but a PC is basically a doorstop in 5 years or less.
Despite my personal bias, I have always used Microsoft products because there was no real alternative. Remember in the early 90s cursing because someone sent you a WordPerfect document that couldn't be opened in any other software? I do and I didn't want to be that guy. The good people at Apple also realized this and when they made their Office equivalent, they went to great lengths to ensure that people could import ppt documents with ease and export presentations in ppt format. Despite this, I hesitated making the switch because of the "unreadable file" prospect that looms over any potential speaker at a conference. I wasn't going to make two presentations (one in PowerPoint and one in Keynote) just to avoid this, so I continued using PowerPoint.
The difference now is that I have a class to put together and I am using my own laptop. There is virtually no way that I might face any compatibility issues here, so I think I am going to create my lectures for class this semester in Keynote. But before I do, I thought I would solicit any advice on potential drawbacks of moving to Keynote. I don't that Mac has the answer for everything, so if I am about to run into a massive pitfall by switching (for class, not international presentations), better to know that now.