I was going to make a new post about this, but here it is already: 'The Perfect Topic' for this post!
I've found that, at a certain time of day, there are a lot of lurkers who are looking for a group, but aren't /lfg. This is a pain in the butt when you are trying to build a group for an LDoN in off-peak times, and is part of the reason they are just lurking -- they don't want to commit to a group until they know it's almost good to go. They especially don't want to commit to a group that doesn't have [insert particular class or capability here].
However, once a group starts to build and you only have a couple of slots left, tells often come thick and fast (if your group is LFP). I was in a situation the other day where it took about an hour to get a group together, but I had to reject 3 or 4 people in the last 5 minutes. This is just ridiculous, IMHO, because we could have been away in a third the time if I'd got those tells early on! And, it gets a lot worse than that.
So, lurkers: STOP BLOODY LURKING! You're making it dull for the rest of us. :)