mongodump v3.0.1 takes approximately 3 days to do an export of my mongodb db of approximately 17GB. When I run mongodump v2.6.9 on the same server and database the export completes in a little over 2 minutes.
checking the mongostat I can see that on 2.6.9 the network out values are generally in the 20-60m range. see attached mongostat.dmp2.6.9.txt
mongostat on the 3.0.1 the network out is constant 10k - 11k. see attached mongostat.dmp3.0.1.txt