My Toyota dealer mechanic, who is also a personal friend, does my oil changes every 5,000km. According to him, the 8,000km thing is really for marketing purposes, and although you can definitely go 8,000 before a change, it makes little sense.
As for oil, he talked me out of using Mobil-1 in my Vibe (Toyota Matrix clone), and suggested a good quality dino oil instead (Castro). I now change my oil at 5,000km or six months, whichever comes first.