With Mawlid un nabi, I know that some people are not sure on its validity. But something strange happens at this time of the year every year:
Some people celebrate mawlid and get on with it.
Then there are some people who dont celebrate it who get on with it.
Both of these groups are trying to act on Islam on the way they consider the the best way to follow the Qur'an and sunnah with sincerity. Both can be deeply admired as long as you are willing to understand the reasons for their views and actions.
But then there is a third way, that I dont get - those that get a pain in their stomach when mawlid is celebrated (with the performing of ibadat, lets not pretend that its because someone might do something that is considered unislamic behaviour).
A person who falls into this third group needs to ask himself why spend so much time and effort to try and stop fellow Muslims from doing ibadat. It's like doing the devils work.