I just upgraded the RAM in my Mac Mini from 512 measly megs to 2 gutsy gigs, and it made a huge difference.
Which was nice.
The inside of the thing was packed as tight as a laptop, as you'd expect, really. So RAM changing is not a procedure for the faint of heart or the heavy of hand, but with care it's an easy half hour.
And I've discovered this, which is also nice:
tell application "Finder"
say "My dog has no nose."
say "Really? How does it smell?"
say "It doesn't, it's got no nose."
end tell