I presume in registering for mumsnet there's a default username of "user" followed by a load of numbers. This really isn't a good default, there's more and more of them now and the number strings are so long it'd be hard to tell one from another if they both post on a thread. Can you not do what the BBC do with usernames and put three words together so at least it's distinctive and memorable? Also the names have no personality whatsoever compared to most self-chosen names.