Ye Gods! Just looked at the stats for Tumblr.
500 million page views a day
15B+ page views month
Peak rate of ~40k requests per second
1+ TB/day into Hadoop cluster
Many TB/day into MySQL/HBase/Redis/Memcache
Growing at 30% a month
~1000 hardware nodes in production
Billions of page visits per month per engineer
Posts are about 50GB a day. Follower list updates are about 2.7TB a day.
Dashboard runs at a million writes a second, 50K reads a second, and it is growing.
And all this with about twenty engineers!