It was great getting to photograph my Aunt, Arlie Mierins. It's always interesting trying to photograph someone that you know so well...
You have to make sure that the photo really shows who they are and you can't let the comfort level get in the way of the capture or the way they are represented. After all, they know you so well the conversation and humor is quite standard and they may not react the way another subject or client might. In addition, as the photographer you cannot allow your perspective of them be what is captured, since the way you view them may not be the same as the perspective the rest of the world has of them!
During most portrait shoots I have a shot I'm really happy with about 20 minutes into the shoot. I keep it going to get the most out of the shoot and the subject, but within 20 minutes I know I have something that represents the client well and that they will be happy with.
When shooting family though, it often takes a little longer because you have to break through the familiarity to get something truly great.