This is most likely a problem with cookie support in your browser.
Again, most browsers should warn against such a thing (this is clearly stated in the HTTP recommendation when discussing POST).
No, you don't have to sign in. If you press the 'submit' button and receive a confirmation you can be fairly sure it is posted.
The forum is moderated every now and then. Posts are deleted rarely (only if they are offensive or so old and out of date, that they become misleading). Sometimes topics are moved from category to category.
Not really:
FAQ - self-eplanatory,
Problemset Archive - problems with your code (and possibly the problemset),
Online Judge System - problems with our code,
Problems with languages - problems with specific languages and/or our compilers,
Extending the Problemset - new ideas and suggestions of tasks to add,
General Discussion - off topic.
All these forums are open - anyone can post, anyone can help out 
.
In some time we will probably drop phpBB and integrate the forum with spoj. Every problem will have its threads, but a general forum will still be available for general discussion (perhaps with a separate category for reporting trouble with the site).
