The majority of git HEAD (eca96d71187ddd053fa3be0e9e396b4a700d9ae0) debug messages on a public node are now from one single source:
[jgarzik@eu3 src]$ wc -l /spare/bitcoin/data/debug.log 7895 /spare/bitcoin/data/debug.log [jgarzik@eu3 src]$ grep -c 'socket send buffer full warning' /spare/bitcoin/data/debug.log 2375
Workaround is obvious, delete the printf() call in net.cpp.