So once that port is opened (port forwarded), what does it actually do for the bitcoin-qt client that's different from before?
Necessary to act as a full node, otherwise you will be limited to 8 incoming connections with no outgoing connections.
Ah, ok. I just opened up port 8333 and noticed that my number of active connections went from 8 to 10. I'm seeing the below entries in my debug log. Is this normal? (I removed my IP address in the log below)
2014-11-10 17:52:33 ProcessBlock: ACCEPTED
2014-11-10 17:52:33 ERROR: AcceptToMemoryPool : inputs already spent
2014-11-10 17:52:33 ERROR: AcceptToMemoryPool : inputs already spent
2014-11-10 17:52:57 ERROR: AcceptToMemoryPool : inputs already spent
2014-11-10 17:52:58 ERROR: AcceptToMemoryPool : inputs already spent
2014-11-10 17:53:00 receive version message: /bitcoinseeder:0.01/: version 60000, blocks=230000, us=x.x.x.x:8333, them=0.0.0.0:0, peer=178.62.20.190:43641
2014-11-10 17:53:00 Added time data, samples 17, offset +0 (+0 minutes)
2014-11-10 17:53:00 nTimeOffset = -1 (+0 minutes)
2014-11-10 17:53:03 receive version message: /bitcoinseeder:0.01/: version 60000, blocks=230000, us=x.x.x.x:8333, them=0.0.0.0:0, peer=199.127.225.232:45435
2014-11-10 17:53:03 Added time data, samples 18, offset +0 (+0 minutes)
2014-11-10 17:53:05 ERROR: AcceptToMemoryPool : nonstandard transaction: dust
2014-11-10 17:53:05 socket recv error Connection reset by peer (54)
2014-11-10 17:53:08 ERROR: AcceptToMemoryPool : nonstandard transaction: dust