The only projects I can actually think of that are based in the US and made by american authors are those by xiph.org, and they only get away with it because their entire business model is developing royalty free alternatives to MPEG codecs.
Even if multimedia patents might not affect big corporations much, they definitely seem to strongly affect the open source community. I imagine if we had similar dystopian laws here in the EU, our best and most beloved multimedia software would plain not exist.