With the current mongodump/mongorestore, it's not possible to copy just one collection from one database to another
(see this thread on mongodb-user: http://groups.google.com/group/mongodb-user/browse_thread/thread/daebd48eca33d3ee)

I expected to do something like this, but unfortunately mongorestore does

a) always use the original DB although I specified the target DB with the -d option (I heard the nightly builds behave different) and
b) always restores the complete DB instead of a single collection.

I thought I could copy over one collection to another DB with something like this:

pinocchio:~ oliver$ mongodump -d services -c suppliers -o tmp/dump
connected to: 127.0.0.1
DATABASE: services to tmp/dump/services
services.suppliers to tmp/dump/services/suppliers.bson
29603 objects

pinocchio:~ oliver$ mongorestore -d services_dev -c suppliers --dir
tmp/dump/
connected to: 127.0.0.1
tmp/dump/services/suppliers.bson
going into namespace [services.suppliers]
read 489874/11917784 bytes so far. (4%) 1028 objects
...
read 11605076/11917784 bytes so far. (97%) 28784 objects
29603 objects