Apple notes that "The Find My iPad feature works best if your iPad includes both Wi-Fi and 3G, but it will also find your Wi-Fi-only iPad when it's connected to a wireless network." Translation: Find My iPad probably isn't going to work very well at all for the Wi-Fi-only models. It'll probably give you a very general idea of your iPad's location on Find My iPad's map, but without GPS capabilities, the Wi-Fi-only iPad will have nowhere near the specificity of the 3G-enabled iPad or iPhone.
Naturally, just like Find My iPhone, Find My iPad requires a $99/year subscription to MobileMe -- though if you're already using the service for your iPhone and/or Macs, there's no extra charge for the new iPad-specific services.
[Via Ars Technica]