Without jailbreak? I don't know, haven't tried. In theory, it is certainly possible. But in theory you can also run complete Debian GNU/Linux on Nokia N900. Which is sortof my point. The UI has to be really optimized for the hardware, and 3rd party software has to be really ported to the hardware (optimized for hardware performance wise, UI wise (think also about software keyboard, lack of mouse pointer)). Else you get a poop user experience. Perhaps with iPad its merely "looks a bit crappy" though.
They're maemo and MeeGo... "Meamo!" sounds like what Zorro would say to catherine zeta jones... after she slaps him for looking at her dirtily...