Some personal examples of ways I've answered the weakness question...

"I was not lucky enough to be born with a natural organization gene, therefore I've worked very hard at developing good organizational habits that have become real survival skills in my career. Things like religious use of a DayTimer, Task Lists, etc have helped me to excel."

"One growth opportunity I see for myself is continuing to develop my ability to deal with folks who are highly risk-averse. In the past I found it challening to partner with folks who dismiss new methods and thinking out of hand. As a result, I've worked hard to develop an understanding of those behaviors so I can help them win and build a relationship in the process. But I think one can never be too good at that so I will continue to work on it."

Be honest. Show self-awareness. Show growth. Be positive.