The basic gist of the - for now - draft agreement is that Twitter promises not to use its patents or its employees' patents in an offensive manner without explicit permission from the people listed as inventors. This applies to both past, present, and future patents, and is strictly transferable; if the patents are sold, the original agreement still stands.
"The IPA is a new way to do patent assignment that keeps control in the hands of engineers and designers," writes Adam Messinger, VP of engineering at Twitter, "It is a commitment from Twitter to our employees that patents can only be used for defensive purposes. We will not use the patents from employees' inventions in offensive litigation without their permission. What's more, this control flows with the patents, so if we sold them to others, they could only use them as the inventor intended."
Currently, the norm in the industry is that employers automatically gain ownership of all patents filed by their employees. These patents could then be sold to another company, which could also do whatever the heck they wanted with them. This potentially puts a damper on innovation, as employees may not wish to contribute to the current sad state of the industry.
The agreement is still being written and finalised, and will be implemented later this year. Ever jaded and cynical as I am, there's a part of me that thinks Twitter did this simply because they have no patents to speak of and as such could use this - for them - meaningless gesture to score some easy goodwill points. However, I'm in a good mood, so let's give them the benefit of the doubt.
Other companies are free to adopt the pledge, but considering how this industry is sick to its very core, I highly doubt the companies that matter would ever sign something like this. Apple, Microsoft, and Oracle will never sign this, since they're currently too busy trolling (although change might be on the horizon). Facebook and Google could potentially be interested in this, and of course smaller companies not yet infested with the patent sickness.
It's a good start, but since it's not a law, it's only worth the paper it's written on. I've never trusted companies and I have no desire to start now, so we'll just see how serious this is for Twitter.