That is, if db is connected to sf1:27017 and you set sf1:27017 to be arbiterOnly in replSetInitiate, the other machines will endlessly spin with:

Tue Jul 27 18:33:43 [rs Manager] replSet info not trying to elect self, do not yet have a complete set of data from any point in time
Tue Jul 27 18:33:49 [rs Manager] replSet info not trying to elect self, do not yet have a complete set of data from any point in time
Tue Jul 27 18:33:55 [rs Manager] replSet info not trying to elect self, do not yet have a complete set of data from any point in time

I started up:
./mongod --replSet unicomplex/ubuntu:27017,ubuntu:27018 --dbpath ~/dbs/blort1
./mongod --replSet unicomplex/ubuntu:27017,ubuntu:27018 --dbpath ~/dbs/blort2 --port 27018
./mongod --replSet unicomplex/ubuntu:27017 --dbpath ~/dbs/blort3 --port 27019

Then ran:
> rs.initiate({_id:"unicomplex", members:[{_id:0,host:"ubuntu:27019"}, {_id:1, host:"ubuntu:27018"}, {_id:2, host:"ubuntu:27017", arbiterOnly:true}]})

test in replsetarb1.js