My host recently contacted me, and said my site was using too much memory and CPU resources. It's a site that makes heavy use of PHP and mySQL. He says that it occasionally jumps up to 15% memory usage, and the CPU usage up around 1.5-2.5. This is on a Celeron 2.2gHz with 512 of RAM. Do those numbers seem unreasonably high to you? Does he have a right to be concerned, or is this within the boundaries of normalcy?