I have always had a soft spot for .nu domains. They were one of the first CCTLD's to be sold for other purposes and I registered hudson.nu in 1998. This means I have had the same email address for 14 years along with a short, memorable, web address - although most of my web pages have now been folded into www.ecalpemos.org and hudson.nu may be email only by the end of the year.
The advantages of .nu include that the public whois does not list the registrant, but it does list accurate technical information. It also has a low tolerance for spamming and reasonably high registration fees which means it is a clean name space with high availability of good names.
I notice from the whois lookup at domaintools.com that there are 49,242 domains associated with support[at]nic.nu.
I don't know if this is the total figure, but it gives some indication of how small .nu is. There are over 100 million active .com domains and over 9 million .uk ones.