I confess i deleted two kids from the second generation when i started playing in the third generation. I just didn't want my main sim to have too many siblings.
I confess i enjoy playing as male sims more then female sims. Which is why i always complain about the lack of hairstyles and clothes for men.
I confess that whenever my sims have a toddler, they immediately become unimportant to me. No matter how good their storyline and personality is, i'll play as the toddler till he/she becomes a boring teenager. Then i'll maybe remember about the elders. Or they'll just have a new child for me to create another huge dramatic story for, which will probably include lots of violence, first crushes, deep secrets, etc. I'm probably alone on this one since usually i hear people don't like playing with kids.
I confess no matter how much i love pets i barely spend time with them. And i definitely never walk my dogs. Except on very rare occasions.
I confess i spend way too much time on playing the sims. Sometimes i don't even play - i just rebuild a shop or something like that.
I confess skipping some life stages in the past.
Finally, I confess using "motherlode" for my sims which were supposed to be rich for the sake of the story. And on sims that weren't supposed to be rich but needed a nice house.