Angel, don't forget the circus skills - jumping through hoops, juggling three reams of paper and a luncheon buffet for six, swinging from the ceiling with a phone in one hand and three diaries in the other ...
As you can see, missylu, it's really more about abilities and coping with stress than with any qualifications. Do the job well enough for one person and your reference will be your qualification for the next job - that's if the boss knows how to write one!
I've worked as PA for a couple of really good bosses - "What do you need me to sign? ... OK, there you are ... I'll go away now and let you get on ..." - but also for a woman who'd walk further to find me, in order to ask me to photocopy one sheet of paper, than she would have walked in the opposite direction to do it herself! It's no exaggeration, Missy, they really can be that lazy/stupid/ignorant.