"There are many articles that suggest that it is unlikely that the company would ever try to enforce its IP agreement, much less succeed. But I was not comfortable entering a situation where the company might in the future claim exclusive rights to one of my "inventions," and prevent me from using it somewhere else.
When it came right down to it, my list of "inventions" looked pretty meager. These "inventions" are not really inventions at all, but rather extensions and adaptations of publicly available software. Using the word "invention" to refer to such extensions is unfortunate; it is an attempt to impose an ownership structure onto software ideas, and contradicts my experience of how software development really works. For the full story, see The Employee IP Agreement."
John kept careful track of his thoughts (and a lot of emails, phone calls and in-person meetings) while he sought to forge an IP agreement that he'd hoped would be workable for him and his client. It's a sobering story, so be thankful he's put it to writing. 1/3 warning, 2/3 good advice.