Signing up for raids is mandatory whether you can or cannot attend. This is to give the raidleader a clear overview of what classes are available and whether a raid is possible or not. Signing up for raids for the designated timeframe will enable you to attend the raid unless it is overbooked in which case the raid leader will select the most balanced raid group. Signing up for raids at a certain day but at a time later than the official start of the raid will give you no certainty of entry. Make sure that if you sign up for time xx:xx you can actually attend at that time and not have to go afk at time xx:xx for 30 minutes or so.
If you signed up as available for a raid you are expected to be in the correct instance at the time specified in the sign up thread. The time stated in the sign up thread is the time at which we start pulling. Being ganked by the Horde is no excuse to be late. Also being in another instance at the start of the raid "just finishing" is not an acceptable reason to be late.
If you signed up as available and something comes up through which you cannot attend make sure to send a private message on the forum to Brutice or notify him ingame.
If you have to go AFK during an instance run make sure you notify the raid leader. If you do not notify the raid leader and are AFK for an extended period of time for no apparant reason you might find yourself replaced. If you have to go quickly AFK just before a pull make absolutely sure that you inform the raid leader to prevent a raid from wiping. To not inform during a situation like this is totally unacceptable.