After updating java driver to 2.12.0 gc activity raises for a several dozen percent. In logs I can find:
May 09, 2014 3:33:36 PM com.mongodb.ServerStateNotifier run
FINE: Checking status of s122712.dc2:27017
May 09, 2014 3:33:36 PM com.mongodb.BaseCluster updateDescription
FINE: Updating cluster description to {type=ReplicaSet, servers=[

{address=s122712.dc2:27017, type=ReplicaSetPrimary, averagePingTime=2883898000000 ms, state=Connected}

]

But ping gives:
ping s122712.dc2
PING s122712.dc2 (xx.xx.xx.xx) 56(84) bytes of data.
64 bytes from s122712.dc2 (xx.xx.xx.xx): icmp_req=1 ttl=64 time=0.322 ms
64 bytes from s122712.dc2 (xx.xx.xx.xx): icmp_req=2 ttl=64 time=0.359 ms

In fact there are thousands DBPort and MongoOptions objects created every second which kills servers in less than an hour.