I only really tried it on the Pandora so far. First thing that put me off was the need to register with Google. Then I was unable to find anything, because nothing was where I expected to find it. Also navigation was somehow not quite as I expected. So after I spend a short time trying to find some settings I decided to just EXIT the darn thing, which took me 30 minutes to figure out how to do.
Granted: the last one is more a Pandora-related problem, since I expect any hardware running Android as main OS will probably be switched off with a button.
But to me it was entirely unintuitive to use from the beginning. And since it does not give me impression I can really DO anything with it, I don't feel any motivation to try and learn how to use it. I felt strangely constrained by it even.
I guess it's all practical reasons, I use Linux at work and have it on my laptop and my desktop PC at home. I can easily switch from one to the other, exchange files, SSH to any of them ... I just can do a lot of stuff, and it works the same on any of my devices. Maybe this is somehow possible with Android (don't tell me I have to buy an app for that though, that would be laughable), but why make things harder if the solution is already there?
I don't hate Android, I just couldn't find anything I like about it.
(And what Exophase said is also true)