Excellent post Wyrmy, and some very good feedback.
I can only agree with what everyone has said. We all have to be willing to step out of a raid when it is not possible for us to go. This happened to me with the RS 25 man. But rule 2 applies - Stick around as sometimes spots open up mid raid. This happened after about 90 minutes (I had actually been listening in on TS, so was following the fight as it was happening - this is also beneficial, especially on a new fight) and I was able to come in and help take down Halion.
I know that I am personally not going to be able to make it to Team Donkey as often this winter due to my work shift pattern. This will make it more uncertain as to whether I will get a spot in the raid as often as I have been. This I totally accept as I know that Team Donkey is the progression raid and needs as much stability as possible. It took several weeks of pounding on Arthas before we actually roflstomped him. This required a good core of the same people so that we could progress. If the raid leader had kept changing the people in the raid every week. Then I know that we would probably be no closer to getting Arthas down. Many raiders are not willing to put the effort in to this kind of perseverance. Please don't think that this is directed at your good self, but others reading this may need to be honest and realise what Team Donkey is actually about.
I would also take the advice Darieth gave you and never unsign if you can make it and want to go. He cannot know that you have unsigned due to thinking you will not get in. Be there and available and you have the chance to go.
Blimey, didn't mean to waffle on so long
Also, Hi Spectrus