It's easy to say yes, and we do it all the time. However, I personally have a lot of trouble saying no, and it's a problem. It misleads people at best, and at worst it makes you look like you can't commit to an answer.
Therefore, I resolve to say no and explain as best I can to people why I am doing so. I find they will take it better if I am upfront and honest, and it saves me the trouble of worrying about it later.