iv been looking at my kernel task, and more to the point, how much memory its taking up.. iv got 4gb's of ram in my leopard sr mbp, and its using 235mb of it with 58 threads. is that usual?
kernel_task has about a 200MB rsize on my system, so that seems normal if that's what you're measuring. rprvt is probably a better indicator, although I wouldn't put a whole lot of trust in it for measuring non-userspace processes.