The majority of git HEAD (eca96d7) 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.