[jbellis]

I would bet that SO has several orders of magnitude less traffic than Digg.

[ratsbane]

Looking at Alexa's numbers for a rough comparison of pageviews it looks like Digg gets about 10x as many as SO:

http://www.alexa.com/siteinfo/stackoverflow.com#trafficstats

[gill_bates]

So while SO runs on a minimal amount of closet-room hardware efficiently and without incident, Digg has heroics and clusters and scale-outs and all sorts of drama to handle just 10x the load? I'm not sure what angle you were coming from, but that makes Digg look like clowns.

[skorgu]

Not saying that Digg aren't clowns but the traffic balance makes a huge difference. It's not implausible that Digg has an enormously bigger fraction of writes to reads than SO does which changes the scaling dynamics considerably.

Edit: To expand I'd imagine SO serves a lot of static "how do I" google hits for logged-out users which is about as easy to serve as it gets. Digg puts a higher emphasis on the logged in experience and commenting which reduces the ability to cache.