Some more data:
I compiled the top 100 list of name servers used by .co domains.
I am too lazy and don't have enough time to comment thoroughly on it but just one remark: most domain names have two name servers that typically go in pair, for example NS68.DOMAINCONTROL.COM. + NS67.DOMAINCONTROL.COM.
In this example you can see the figures almost match. Sometimes people mix different name servers, which can lead to inconsistent resolution.
Basically that means 40K .co domains would be using the NS67/68.DOMAINCONTROL.COM pair.
Then 30968/30969 domains using NS55/56 etc.
As you can see, a lot of .co domains are using Godaddy DNS, as outlined in a previous analysis. If I remember well more than a third of all registered .co domains were pointing to Godaddy nameservers.
That doesn't mean all those domains resolve to Godaddy parking pages, because some people host the DNS at their registrar and set their own A/MX records etc from there. A more accurate breakdown could be achieved by resolving each domain to IP (A) addresses.
Nonetheless I assume most of those domains are effectively parked and idle.
If you just consider the domains on Godaddy nameservers it looks like they might account for 50% of .co volume (but I am bit tired now).
This might highlight a huge pattern of non-development in the TLD.
Code:
40004 NS68.DOMAINCONTROL.COM.
39999 NS67.DOMAINCONTROL.COM.
30969 NS55.DOMAINCONTROL.COM.
30968 NS56.DOMAINCONTROL.COM.
30679 NS30.DOMAINCONTROL.COM.
30678 NS29.DOMAINCONTROL.COM.
30154 NS63.DOMAINCONTROL.COM.
30151 NS64.DOMAINCONTROL.COM.
29447 NS2.SEDOPARKING.COM.
29438 NS1.SEDOPARKING.COM.
27699 NS2.PARKCO2.NEUSTAR.BIZ.
27699 NS1.PARKCO2.NEUSTAR.BIZ.
27420 NS2.PARKCO1.NEUSTAR.BIZ.
27420 NS1.PARKCO1.NEUSTAR.BIZ.
25995 NS.CONFICKER-SINKHOLE.ORG.
25995 NS.CONFICKER-SINKHOLE.NET.
25995 NS.CONFICKER-SINKHOLE.COM.
24705 NS02.CASHPARKING.COM.
24705 NS01.CASHPARKING.COM.
24285 NS62.DOMAINCONTROL.COM.
24282 NS61.DOMAINCONTROL.COM.
21278 NS52.1AND1.COM.
21278 NS51.1AND1.COM.
19963 NS2.123-REG.CO.UK.
19962 NS.123-REG.CO.UK.
19744 NS70.DOMAINCONTROL.COM.
19744 NS69.DOMAINCONTROL.COM.
19381 NS23.DOMAINCONTROL.COM.
19373 NS24.DOMAINCONTROL.COM.
19222 NS74.DOMAINCONTROL.COM.
19222 NS73.DOMAINCONTROL.COM.
19180 NS08.DOMAINCONTROL.COM.
19180 NS07.DOMAINCONTROL.COM.
19055 NS37.DOMAINCONTROL.COM.
19054 NS38.DOMAINCONTROL.COM.
18223 NS20.DOMAINCONTROL.COM.
18222 NS19.DOMAINCONTROL.COM.
17732 NS42.DOMAINCONTROL.COM.
17728 NS41.DOMAINCONTROL.COM.
16775 NS22.DOMAINCONTROL.COM.
16769 NS21.DOMAINCONTROL.COM.
16415 NS15.DOMAINCONTROL.COM.
16414 NS16.DOMAINCONTROL.COM.
16235 NS66.DOMAINCONTROL.COM.
16234 NS65.DOMAINCONTROL.COM.
16164 NS77.DOMAINCONTROL.COM.
16163 NS78.DOMAINCONTROL.COM.
16149 NS50.DOMAINCONTROL.COM.
16147 NS49.DOMAINCONTROL.COM.
16115 NS72.DOMAINCONTROL.COM.
16115 NS71.DOMAINCONTROL.COM.
15979 NS14.DOMAINCONTROL.COM.
15978 NS13.DOMAINCONTROL.COM.
15604 NS67.1AND1.CO.UK.
15603 NS68.1AND1.CO.UK.
15489 NS75.DOMAINCONTROL.COM.
15487 NS76.DOMAINCONTROL.COM.
15415 NS10.DOMAINCONTROL.COM.
15414 NS09.DOMAINCONTROL.COM.
15221 DNS2.NAME-SERVICES.COM.
15221 DNS1.NAME-SERVICES.COM.
15202 DNS3.NAME-SERVICES.COM.
15192 LOCA244235.VENUS.ORDERBOX-DNS.COM.
15185 DNS4.NAME-SERVICES.COM.
15180 LOCA244235.MERCURY.ORDERBOX-DNS.COM.
15056 NS11.DOMAINCONTROL.COM.
15055 NS12.DOMAINCONTROL.COM.
14735 DNS5.NAME-SERVICES.COM.
14268 LOCA244235.MARS.ORDERBOX-DNS.COM.
14255 LOCA244235.EARTH.ORDERBOX-DNS.COM.
13672 NS05.DOMAINCONTROL.COM.
13671 NS06.DOMAINCONTROL.COM.
13636 PARKCT2.SECURESERVER.NET.
13636 PARKCT1.SECURESERVER.NET.
12761 NS3.VPWEB.COM.
12757 NS2.VPWEB.COM.
12754 NS4.VPWEB.COM.
12349 DNS2.REGISTRAR-SERVERS.COM.
12348 DNS1.REGISTRAR-SERVERS.COM.
12345 DNS4.REGISTRAR-SERVERS.COM.
12345 DNS3.REGISTRAR-SERVERS.COM.
12017 NS2.LIVEDNS.CO.UK.
11984 NS1.LIVEDNS.CO.UK.
11849 NS3.LIVEDNS.CO.UK.
11474 PDNS01.DOMAINCONTROL.COM.
11469 PDNS02.DOMAINCONTROL.COM.
10984 DNS5.REGISTRAR-SERVERS.COM.
10350 NS2.NAMERESOLVE.COM.
10350 NS1.NAMERESOLVE.COM.
10251 NS36.DOMAINCONTROL.COM.
10251 NS35.DOMAINCONTROL.COM.
10140 NS3.NAMERESOLVE.COM.
10109 NS4.NAMERESOLVE.COM.
9596 DNS010.D.REGISTER.COM.
9581 DNS249.D.REGISTER.COM.
8362 NS33.DOMAINCONTROL.COM.
8358 NS34.DOMAINCONTROL.COM.
8119 NS2.ALLSAFEHOSTING.COM.
8119 NS1.ALLSAFEHOSTING.COM.
7977 NS66.1UND1.DE.