I don't think AROS and Haiku will be direct competitors, since they aim at different usergroups. However, like AROS, Haiku is well worth while the look.
Yes and no. I think both AROS and Haiku have two distinct groups of potential users: those that were enamoured with the old system (Amiga OS and BeOS respectively) and want to see it continue, and those who aren't satisfied with the current mainstream options (Windows, Mac and Linux) and are looking for something better but don't necessarily have any emotional attachment to a platform. Haiku and AROS are definately competing with each other for users in the latter category. I should know as I'm mostly in the latter category and I held an interest in AROS for a while, but ultimately I've moved on to a different alternative open source OS.
However, I didn't turn to Haiku. My interest currently lies in a OS called Syllable. It's not a BeOS clone, but it gets a lot of its inspiration from there. From my perspective at least, it's quite a ways further along than AROS or Haiku, but it doesn't seem to get nearly as much attention (presumably since it isn't a clone of an existing system with a rabid fan base). If you're interested in alternative OSes it's definately worth checking out:
http://www.syllable.org/Personally, I don't think AROS will go very far outside of the core Amiga fanbase. Amiga OS was a great OS for it's time, but I have a hard time thinking of any virtues it had that aren't handled better in other alternative OSes. I'm not entirely convinced Syllable will really go anywhere either, but at least it's not hobbled by 20 year old design decisions.
