The "add-to-list" line for some reason is not enough to automatically activate the arc-mode for *.arc files, although I can activate it manually by doing M-x arc-mode.
By adding a variation of your snippet to my .emacs, I got arc-mode to activate automatically:
here is a recap of what has happened in arc over the past 12 hours.
some excerpts:
* ams has joined channel #arc
<ams> i'd like to rewrite linux in arc, where do i start?
<mattl> arc is certainly capable.
<ams> and it is a exploratory language, so it shouldn't take to long
<bgeron> I'm not so sure about that
<ams> are you saying arc is not good?
<ams> why not? why can i not write linux in arc?
<ams> pg says it is the best language out there
* wvd has joined channel #arc
<wvd> hello
<wvd> I'm starting a company, I'll call it bizarro google and instead of hiring CS and math phds I'll hire only cobol programmers. I'm sure Y combinator will give me venture capital for that.
<wakeupsheeple> can i be co-founder
<wvd> what will your business focus be?
<wakeupsheeple> we will consult companies with solutions for their webapplications based on 'software as a service', providing content to their users
<wakeupsheeple> wvd what should i name my web 2.0 company, Quaykor or Kwxxypp
<wvd> totally go for Kwxxypp, vowels are for the weak
<wvd> register the domais kwxxypp.ru, that way people wont think that kwxxypp is just some random string of letters but instead that they might have some kind of non-unicode browser that does not render cyrillic URLs
<wakeupsheeple> your first duty as Kwxxypp cofounder is to register that domain since i've already posted the business plan here
