Considering the topic of discussion, how sure can you be that archive.is will still be around in a year? Three years? Ten?
As much as I tried, all I could find about it is that it's run by one guy in Czech Republic who's paying $2000/month out of pocket for hosting, and apparently dislikes Finland.
http://archive.is/robots.txt doesn't seem too bad, it looks like you could slowly inhale everything... in theory. There are no sitemaps (they're there, but empty placeholders); you have to know the site name to be able to get a workable list.
I think http://www.webcitation.org/ might be better in that regard since it's a consortium of "editors, publishers, libraries". See "How can I be assured that archived material remains accessible and that webcitation.org doesn't disappear in the future?" in their FAQ (http://www.webcitation.org/faq). Although from my perspective it seems to be more geared towards academic use.
archive.is is very nice, but they're a URL-shortener as well, so their links are utterly opaque strings of alphanumerics, whereas the Wayback Machine preserves both the full original URL and the date and time it was captured in the archival URL.
archive.is does not crawl automatically, it must be pointed at a page by a user. While this makes it particularly useful for snapshotting frequently-changed pages, it is not a replacement for the proper Internet Archive.
