Are anime streaming sites legal? I don't think it should concern me, but I am still curious as to how legal anime streaming sites are. A popular site being AnimeUltima, I've watched probably 300+ different anime just from there. However, when asked if the site I use is legal, I usually respond with, "yes," despite not knowing the answer; this is sort of annoying in itself.

AnimeUltima as an example, is this site legally subbing and uploading anime?
There are a number of legal streaming sites: Crunchyroll, Funimation, Manga Entertainment, Daisuki (which is relatively new), and some Youtube channels associated with legal sites (such as Funimation or Manga Entertainment), possibly among some other sites that I haven't heard of yet or am not completely sure about. Some of these are very region-specific (e.g. a lot of Funimation videos on Youtube can't be accessed outside of North America (I think)).

Most other streaming sites (including some pretty popular ones, it seems) are actually not legal (using, as stated by @Oded, rips of videos from elsewhere, illegal fansubs, etc.).