Recently, I've been looking at PhoneGap. However, unlike most people at Nitobi, I am using a PC. However, I spend most of my time running Ubuntu Hardy Heron on my dual-boot system. This means that unless I wanted to jailbreak a phone, there's really no way that I could do iPhone Development. However, the other day I decided to start taking a look at the Android SDK when the G1 was announced. It'll be a while since we'll get any Android phones in Canada (for more info, read this), it'll be good for the rest of the planet to have the ability to write once and run anywhere. Sort of like what Dave said.
This also hasn't been merged into the official repo yet, and currently lives on my GitHub: https://github.com/bowserj/gap/ It's been a while since I've hacked on Java, so the code is probably cruftier than it needs to be. It'd be interesting to see where this platform goes.