Just because its open source doesn't mean that IP terms still can't be brought against you. Here's a simple example. Lets say that someone contributes someone else's patented algorithm into gcc. Now you ship gcc, not knowing about the patent infringement. All of a sudden you have a patent lawsuit on your hands.

This is probably the biggest reason why companies, like Microsoft, even when they do open source, don't accept contributions. Just because someone contributes specific code, doesn't mean they have the legal right to do so.

Sun showed that Java could be a timebomb. And in the hands of Larry Ellison, I think Google is just the first victim. Oracle will be going through uses of Java with a fine-tooth comb. Get your duck in order now.