Some quick first impressions, in no particular order (I'll write a more extensive review once I've actually worked with it for a while):
File transfer is somewhat awkward. You can get presentations from a Mac to the iPad via iTunes easily. The other direction, oddly, does not seem to be supported. I made a simple one-slide presentation on the iPad and the only way I found to transfer it to the Mac was by emailing it to myself.
Keynote on the iPad only supports presentations created with iWork'09. I tried transferring my Webspam presentation, but Keynote on the iPad refused to open it.
Fonts can be a problem. According to the FAQ, Keynote on the iPad
supports over 40 fonts and font families which can be used with iWork for iPad apps. If the font you used to get a certain effect is not among them, things may not look as good as expected ...
The screenshot demonstrates another issue: Links are not supported by Keynote on the iPad. While I could accept that, I hate that instead of silently dropping them, it turns them into text which then completely messes up your slide. Either support them (why not, btw?) or strip them out entirely, but don't mess with my slides!
Please email me for details.