In early 2002, Open Diary changed to a pay site, with a limit of 10000 users. However, there is now Free Open Diary, which is a lot like the old Open Diary.
Unfortunately, there is a ridiculous amount of pop-ups, and their frequency makes the site difficult to stomache. Also, they have stopped accepting new members, and delete diaries if they are not updated within a fortnight.
Many people have switched to alternative sites, such as Diaryland or Livejournal.