Got a shiny new system with 4 GB ram. I haven't installed too much on it yet, so /usr only has a gig or so in it, but it's cool to be able to cache all of it.
% time du -s /usr
1055912 /usr
du -D -s /usr 0.08s user 0.72s system 4% cpu 19.991 total
% time du -s /usr
1055912 /usr
du -D -s /usr 0.06s user 0.11s system 97% cpu 0.172 total
% free
total used free shared buffers cached
Mem: 3632284 205500 3426784 0 32976 67444
-/+ buffers/cache: 105080 3527204
Swap: 2650684 0 2650684
% time find /usr -type f 2> /dev/null | xargs cat > /dev/null 2>&1
find /usr -type f 2> /dev/null 0.04s user 0.10s system 0% cpu 2:11.43 total
xargs cat > /dev/null 2>&1 0.22s user 4.65s system 3% cpu 2:25.38 total
% free
total used free shared buffers cached
Mem: 3632284 1196660 2435624 0 45052 1041212
-/+ buffers/cache: 110396 3521888
Swap: 2650684 0 2650684
% time find /usr -type f 2> /dev/null | xargs cat > /dev/null 2>&1
find /usr -type f 2> /dev/null 0.04s user 0.10s system 18% cpu 0.766 total
xargs cat > /dev/null 2>&1 0.15s user 0.69s system 98% cpu 0.847 total
"What does this mean?", you ask. It means that whatever fraction of time I used to have to wait for a program to load its code from disk, I now have to wait less than one one-hundredth of that while it loads its code from memory.