The best time to make changes to something is during times of change. If you know your name isn't marketing your products to the right target market and need to change it, the best time to make that change is when everyone is watching, such as when you're recently awarded $12 million in venture capital funding.
If no one is watching and you change your name, there is a very strong likelihood you could skip away into obscurity. If no one was paying attention, there will be no transition of existing brand loyalty and brand recognition to help keep you afloat.
The name "StackOverflow" speaks to programmers, but it is meaningless to non-programmers. Non-programmers know "StackOverflow" as some wierd, obscure programming term. If you're a Motor Vehicle Repair enthusiast and your friend tries to convince you to join this Q&A network that was originally a Q&A site for programmers called StackOverflow, they may look at you like your crazy and pretend they never got your email invite to the private beta.
The reason for the name change was to fit the contours of the other Q&A sites that have absolutely nothing in common with programming. It was a strategic decision, and it was the right decision.
It's important to understand that the famous programming Q&A Site, http://stackoverflow.com, is still called Stack Overflow. The company changed it's name, not the Q&A site itself.
I am working on one of the newest Q&A sites, targeted at project managers. Project Management Stack Exchange is in public beta and has some great, experienced users who are able to help answer your professional project management question. If you have project management experience, we could use your expertise. Sign up for an account today!