Works great on my iPod Touch.
Any plans for MA3 for the iPod Touch/iPhone/iPad?
At this point, I don't know. I think they looked at the hardware of the iPod Touch and iPhone (all but the 3GS) and found it was not strong enough to handle Marine Aquarium 3. I'm sure they'll evaluate things and see what makes sense.
Although since MA2.6 and MA3 are quite different, even in the Mac version, this could take more time than they'd ever make back on sales. They'd be splitting the market into MA2.6 for iPhone, iPhone 3G, and iPod Touch and MA3 for people owning an iPhone 3GS, iPhone 4G, or iPad.