What are some IP-related mistakes easily avoided by startups?

I once got a call from a startup that their angel financing wouldn't go through until they had some IP in place which we did on a very accelerated basis, so that company didn't think about IP much in its early stages. Not knowing can blindside you; for patents the US has a 'grace period' but everywhere else in the world once you disclose your invention you can never get a patent on it. Software OS licenses like GPL are a more complex minefield; many OS licenses have a 'copyleft' provision that makes your own modifications also OS. Once your software legitimately falls under an OS license I'm not aware of any way to take it back - the only option I know of is to rewrite your program as a non-OS version. Fork and exec architecture can avoid that for the GPL but more generally programmers need to be cognizant of the specific OS terms that cover the code they're building from if they don't want the OS license on their own work. Usually if the GPL applies it does so for the entire program, not just pieces of code. IMHO, patent your key ideas regardless of whether your software that reflects that invention will be OS; you can still assert that patent against (most of) the non-OS community that might modify your software but avoid subjecting theirs to the OS license.
That help any?
Jerry