How many active nodes in the Bitcoin network?

[disclosure]

Has anyone been able to get the number of active nodes in the entire Bitcoin network?

There were some effort made in this area a while back but no recent/updated data:
1) https://bitcointalk.org/index.php?topic=2346.0 (https://smsz.net/btcStats/bitcoin.kml) - no longer updated
2) http://bitcoinstatus.rowit.co.uk/ - no longer updated
3) http://www.bitcoinmap.com/ - no longer updated
4) http://www.weusecoins.com/globe-bitcoin/ - gone

Blockchain.info has this but only shows nodes that they are/were connected to:
http://blockchain.info/nodes-globe?series=onlineNow

[disclosure]

I am looking for a rough number of active nodes with port 8333 open.
Wouldn't a recursive getaddr be able to do this?

1) https://en.bitcoin.it/wiki/Protocol_specification#getaddr
2) http://nmap.org/nsedoc/scripts/bitcoin-getaddr.html