Matt has put together a tool to easily access (most) of the WordPress.org Plugin stats API using a simple GET string. It returns data back as JSON, and you can see the docs + example at http://api.uproot.us Though the functionality is dependent on the future availability of the endpoint at uproot.us (I wish the source for the API was available), I can see lots of possibilities for plugin developers.
Drew has put together a tutorial to optimize your Apache VPS for WordPress that is worth a looksee if you are running a small VPS and need that extra oomph.
Lastly, via Zedomax, I came upon a small tweak for MySql that could (and has in my case) dramatically improve MySql performance. Check out Angsuman’s tip and explanation if you are interested. Be forewarned that this might have other impacts on your MySql depending on the amount and type of load and queries, but it is definitely worth a shot. Moral of my story is that inserting into the database on every page init can be costly! Now I wish there was a way to accumulate inserts programmatically.