In order to allow new users to sign up again, I have had to make a slight change, which possibly won't be very popular but hopefully won't stay in place for long – at least for regular users.
To re-cap, the reason new users were unable to sign up was because a high proportion of signups were from people whose sole intention was to write a couple of nonsense entries that contained only links and keywords to try to leverage the PageRank DearDiary.Net has with Google for the purpose of increasing their ranking on their spam products. Clearly we're not intending to be a part of that!
However, there have been legitimate people who want to sign up and couldn't – and with some other things going on here I have re-enabled new users, but have disallowed the inclusion of any links in diary entries. This probably won't affect most people, but if it does, drop me a line and I'll make some extra modifications.
Ultimately I intend to automate the 'link banning' system to allow the system to decide whether you can put links in based on the number of previous posts you have, the length of time you've been a member and a few other things that should improve the situation.
But let me know if this causes you a problem!