I've mentioned Slideshark before - it's a great resource if you want to share PowerPoint presentations to your iPad. I've been using it for a while now, and I think it's particularly useful. Simply create your .ppt as usual and then upload a copy of it to their servers. Then open Slideshark on your iPad, sync with your account and it will download the presentation directly onto your iPad. You can then edit the presentation to move/drop slides although you can't yet edit the presentation itself. I also like the fact that you can present one thing to your audience, while displaying an entirely different dashboard of information on your iPad - such as time taken, time per slide and so on. Also, by simply holding your finger on a slide the audience will see the red dot, allowing you to emphasis what you're showing them, without fussing with laser pointers.
There's a commercial version, which gives you more space to store your presentations, but you can simply use the generous space provided for free and delete presentations you no longer need. If you have an iPad, and you think you might want to use it for presentations, give Slideshark a try. I have a personal recommendation URL which means that if you apply using it they will give us both an extra 25MB for free. And, in the interests of complete transparency, if you sign up quickly enough, you may (stress may) win us both $20 vouchers for Amazon.
So, give it a go, and take a look. http://www.slideshark.com/r?r=532382