Buaah, all these sad littles frequent flyers in here who don't want to hear the same jokes over and over again and how unprofessional blabla.

As much as I understand this you should note that most pax on a plane fly quite seldom and are more then nervous. A joke once in a while lowers the tensions and get people to listen. Of course, too many jokes in one sentence is clearly too much or "bad" jokes, but why not add a funny line or two in the security announcement.

People relax and shows the FAs are in a good mood.

I've been flying Virgin blue lately and they handled these things very well. A FA was even singing a nice song over the speaker.
Infamous lines like "Cpt Kangaroo will bounce us now to the gate, plase reamin seated" or what I heard on such a flight "Do not smoke in lavatory, we installed smoke detectors and video cameras to observe activities in there" or just nice additions.

W