As a Project Manager, I know business is not just about facts and figures, but it's all about people and their ability to interact and collaborate. People who are conscious of this reality will often have a natural tendency to be nice to encourage positive mindset around them. In reality, nice is not that positive after all: You are perceived as someone who does not say "no!" and you get dumped on for work tasks; You are perceived as someone who is not confrontational so your problems don't get resolved; you are perceived as someone who is quiet so your opinions are not heard and others define issues.
The list could go on forever, but in short: Nice Is Commonly Exploited. Instead, what you want to be, is be likable: You can say "no!" in a pleasant way; you voice your concerns without necessarily raising your voice; you can resolve issues by searching for solutions even through confrontation when required. I am a likable person (no, seriously, I am) and I like to work with likable persons, much more than I like to work with nice persons. What label do you have in your company?