Just like the gas mileage for a car, a laptop's performance and battery life will vary according to how you use it. Beyond your processor, memory, and hard drive, we've outlined a number of other features that can affect how your laptop performs.

An ATI GPU
Graphics
Less expensive laptops often have an integrated
graphics processing unit (GPU), which leans on system memory (RAM) to render graphics. A higher-end laptop typically has a discrete GPU that acts like a tiny, self-contained video processor. A discrete GPU can free up the RAM and let the processor work faster, but it can also take a heavy toll on battery life.
Networking and Wi-Fi
Staying connected can be as vital as breathing, but it doesn't come for free. Leaving a laptop's Wi-Fi or Bluetooth activated will usually decrease performance and chew up battery life. If you're not plugged in to a wall socket, deactivate your connections when they're not in use.

An external DVD burner
Peripherals
Whether it's a modem or an external hard drive, whatever's hooked up to your laptop via PC Card slot, FireWire, or USB port will draw power and shorten battery life. Some devices will automatically shut down when not in use, but others are power hogs. The best bet: don't connect your peripherals until you need them.
Operating system
Books have been written about how to tweak the effect of an operating system on performance. We don't have the space to get into all of that here, but be aware that you can adjust performance factors in the Performance Options window (on the Advanced tab of the System Properties window). In addition to adjusting the virtual memory level, you can change the processor's priorities and optimize graphics.

Windows performance options