I did for a while. It made me think about the question a lot. I think the meaning in life is something that people feel is there, but when you really look, it fizzles away. However, luckily I feel that I found an answer to the question. My answer is: to benefit the lives of those who would exist irrespective of my existence.
As for the reasons why I arrived at that answer, it's probably better to read an article I wrote about it: http://journalofinterest.com/essays/meaning-of-life/
What are the downsides?