"Preload is a Linux daemon that stores commonly-used libraries and binaries in memory to speed up access times, similar to the Windows Vista SuperFetch function. This article examines Preload and gives some insight into how much performance is gained for its total resource cost, and discusses basic installation and configuration to get you started."
It's easy to use in Ubuntu, just do:
sudo apt-get install preload
...and your performance should increase after preload "learns" your usage habits. Pretty neat program, I must say. Here's some benchmarks: