Thanks for the replies guys.
EVH, as I said earlier I have already carried out a full format and reinstall, followed up by Software Update. This didn't help any. Video stutters like crazy, and pixelates badly, when anything tries to open or run in the background. This is especially apparent using VLC, but also happens with QuickTime X.
I'm having to force-quit applications several times a day, so something is clearly up. When single-tasking the machine is actually quite decent, and I enjoy using it, but a £1,000 laptop shouldn't choke and die when you try to open a plain-text file while watching a movie.
I'll take it into the Apple Store and see what they have to say. Seeing as the CPU barely gets above 5% usage, and the RAM is half-unused, I'm suspecting the hdd may be faulty. That, or the new on-die gfx are just plain inadequate.
EDIT: I forgot to add, my trackpad doesn't seem very sensitive towards the bottom. Literally to the point where I have to make movements four or five times before the screen/cursor picks up the movement. As above I'll see what the Store has to say, maybe I just lucked out and got a duff machine.
That sounds like a very faulty machine. I would take it back asap.