My recommendation to anyone regarding Keynote is that if your main focus is creating and giving live presentations from your own computer, then Keynote will make you stand out from the crowd and can really help to make your presentations memorable.
However, if you need an app that's 100% PowerPoint compatible so that you can easily share documents with others (because they'll be doing the presenting or for training purposes, etc.), then the most PowerPoint compatible presentation out there IS PowerPoint and you'd be doing a disservice to yourself by using anything other that that or at least one of the apps that's trying to be as PowerPoint-like as possible (like OpenOffice).
Another option if you REALLY want or need to use Keynote (because you don't own Office, or don't want to use one of the free alternatives), is to keep your presentation very simple. In this instance, try to convert your charts to flat images before exporting to PowerPoint. This will mean you lose the ability to edit them to make minor changes (and if you're using a patterned background, you may need to change to a plain one). But, even here, if you're forced to keeping your presentations simple AND preparing a slide so that it will look better in PowerPoint, then maybe for your needs, PowerPoint is the best thing.