I think at this point it's mostly of interest to security researchers and malware writers. It's not hard to imagine malware using this technique to transfer data out of an infected VM in a difficult to detect manner. If you can infect enough VMs it might be worth it. Also, this type of technique could be interesting to government employed malware writers.

Another interesting way to exfiltrate data is via DNS. Few networks block DNS, so you can set up a protocol on your own DNS server to transfer data.

The bandwidth is pretty decent, too.

I'm still surprised how well this classic attack works. I've seen $100k IDS and firewall packages not detect this.

I use this personally. Works behind captive portals sometimes too: http://code.kryo.se/iodine/