I though I'd ask the question first before claiming there to be a memory leak issue. I still think there is one though. Its very small but its there. As of now Dolphin is taking up 1.428GB of RAM.I don't remember Dolphin taking up over a gig of RAM but I could be wrong about that...
It would depend. When I run it on my laptop it usually won´t go over 400 MB of usage.
A while ago there was a known memory leak, and I'm not sure if anyone fixed it, as the developers knew anybody who had a computer capable of running Dolphin well probably had enough RAM for the leak to be a non-issue. The devs like to prioritise the most important or interesting problems, as they're making Dolphin in their free time, so tracking down and eliminating a memory leak probably doesn't appeal to them when there are other things to do.