Now is the time of year to review material, including speeches. To be honest, you should keep speeches under constant review, but the turn of the year serves as a good reminder. Think about any speeches that you deliver regularly. Consider the stories, the people you mention, the examples you give. Are they all still relevant to your audiences? Although we get older every year, our audiences don't, so it's important to keep an eye out for material that should be retired gracefully.
Not only should we be chucking out material, we should be incorporating new stuff. There will have been many things that happened to you in 2008 that could make a strong point about your topic. Provided you have been making notes (you are keeping that story file up to date, aren't you?), then you will have a wealth of information to draw on.
How much to change? Well, it depends on your topic. If you talk about technology, you might have to replace more than half the content of your speeches every year. If you talk about leadership, then maybe only twenty per cent of your content needs to be let go and replaced with contemporary examples. Whatever you speak on, make sure that you do change at least some elements of your speech regularly. If not, you will hear your audience saying "I bet they gave that same speech five years ago - they clearly don't care about us any more".