From what I have seen, Canonical doesn't plan to release Ubuntu for mobile devices until 2014.  That's a long time, just think back to how much smartphones have changed in 2 years.  Android meant 2.0 Eclair back then.  What is the Android OS going to look like in 2 more years?  Dunno, and neither does Canonical, which could make it pretty challenging to hit a moving target.  Also, Google just purchased Motorola, so that's one manufacturer that won't be putting anything but Android on their hardware.  Of course, things could change in the other direction as well.  After all, remember when Blackberry was THE choice for business users?  Or Nokia when had huge market share?  Those were both reality just a couple of years ago, so who knows what unforeseen events will occur between now and when there are Ubuntu mobile devices.  I think it will be interesting to see what happens.  Assuming it actually is released at some point, it will at the very least offer another option, and as jimlynch pointed out, choice is a good thing.