I'm a flight instructor that recently purchased a Motorola Droid (with Android OS). I have at least 4 other students have recently aquired a Droid phone from one of the major carriers. In fact everyone of my students (10 total) now have smartphones. It is nearly a dead even split between the Droid smartphones and the Blackberry's. I've had the discussion with two students and we all agree that Logbook Pro would be a convenient and smart purchase if it were available in these two formats. In contrast I don't even know a single student or pilot that passes through our flight school that uses Logbook Pro on their Windows OS phone or Palm PDA. That's my two cents. I'll definitely recommend Logbook pro if the developers take a step forward with this. Contact me if you like someone to potentially test the Beta version.
Just remembered I do have one student with an I-phone. Another thought would be with all the new full html browsers that are coming out on the new smartphones, why not make intergrate Logbook Pro to be fully intergrated into a website that could be acessible from any computer with Internet access, (AOPA recently did this with their Flight Planner, it's brilliant). You can take it one step further and make a simplified Mobile phone browser friendly version in addition, you would never have to worry about keeping software compatible with mobile phone Operating Systems. It wouldn't be quite as accessible (due to poor service areas), but it would be usable... and still more convenient than carrying a logbook. I would use it!