A lot of users register accounts on this site for the sole purpose of spamming. One of my usual "maintenance" tasks is to delete all inactive accounts more than 1 week old. These are accounts that were requested by users, but were never activated after receiving the confirmation e-mail. Most often, these types of accounts are created either by scripts, or by people using fake e-mail addresses during registration.
There are a whole lot of other accounts that are created and activated, but then then go forever unused. Most of these are created with the intention of spamming, but because I have decent spam controls on my site they give up and move on to easier targets. Since I'd prefer not to have a whole lot of unused, potentially malicious accounts sitting out there indefinitely, I'm going to begin deleting all accounts that have not been used since initial activation and are more than 3 months old.
In the (unlikely) event that any legitimate visitors are affected, please just create a new account. I apologize for the inconvenience.