There was a discussion about this here on HN when they announced this naming change. At the time it didn't make sense to me and it really still doesn't. The Nightly, Alpha, Beta, RC standard is pretty ubiquitous and I think it's just confusing to swap out one of the terms with a new one. I knew about the name convetion change and I still saw this title and was perplexed for a moment.
Not really. I don't think most people have ever heard of Arora. I've been tracking browsers pretty closely for a dozen years or so and I've never once run across someone talking about Arora. I did look it up after reading your comment here and it appears to be a mostly still-born effort.
I don't use it, but I'm glad that there's a competitive marketplace in browsers again. Here's hoping some of the better ideas are shameless stolen by Webkit and the Safari team.
They really need to call it alpha - or something else so that the users will not need to do a search to figure out what it means.