I have to disagree. I've had a long career in software development and I've never seen a clause this broad. If the clause was restricted to the term of employment, that would be one thing, but insisting that they own your brain beyond the time that they're even paying you is too overreaching to even consider.
As an appeal to authority, take the Confidentiality and IP Assignment Agreement generated by Goodwin Procter's Founders Workbench. It contains a much more exhaustive (and better) definition of assigned rights, and the obligation to disclose them survives indefinitely. It also is rather more nuanced, so it might not be readily apparent that it in fact is a much stronger assignment clause than the one criticized by the OC.
"I will promptly communicate to the Company ... during my period of employment, and I agree that any such invention ... shall be presumed to have been made during my period of employment..."
Wouldn't a simple assignment clause during the employment term be both clearer and provide the same rights?
The notion that a company owns you is just silly IMO. They make a big point of informing me once a year that I am employed at will and can be terminated at any time for any reason or no reason. So I am clear with them that outside of my work week, everything I do is mine. This is business.
I don't really see the link with free software either, preserving the right to use one's mind, the single most important thing a developer has, seems very important no matter what.
I've never once been asked if a previous IP assignment agreement of this sort is in force when taking a new position.
Again, I don't like competitive restrictions -- I don't even like proprietary software business models! -- but if you are in that game, then this kind of risk allocating language is reasonable in that context. Refusing to sign a contract because of this clause means you are perhaps a closeted free software advocate (and good for you!) or do not really desire a long-term career in this (arguably exploitative) industry.