My team was initially acquired; we were originally a small company in a cornfield in Illinois called Teamprise, where we built the original TFS plug-in for Eclipse. At the time, we were Eclipse Foundation members and reasonably happy about it. Certainly it was nice to give back (in terms of membership fees) to a project that we were a part of and took advantage of. And the Foundation has a few really solid employees and it was nice to talk to them about tech stuff.
But our larger goal in joining the Eclipse Foundation was largely unmet, which was to actually partner. For example: we hoped to bring in a contractor who could occasionally tackle some bugs in Eclipse on AIX which ultimately affected our customers. We were a tiny company and going deep on some weird problem that only affected the Motif AIX build was not particularly rewarding. So we hoped to engage the Foundation to help us out here: we would pay this contractor if they could help us find them. But we were rebuffed in a manner that I found rather off-putting.
Despite this, after we became part of Microsoft I still pushed for us to join the Eclipse Foundation. I stopped pushing when Microsoft had a booth at Eclipse Con one year and a member of the Foundation (apropos nothing) went on a nice, long rant about Microsoft. I don't think it's particularly classy to make fun of your competitors, nor do I really appreciate inculcating an "us vs them" mentality. But to do that after we had paid a big hunk of money to sponsor that conference seemed particularly poor form, and if the Foundation is going to make fun of the people who are paying to sponsor their Conference, what does membership buy you? A steaming pile on your doorstep once a year?
In any case, that was when I stopped advocating for Microsoft to join the Eclipse Foundation and instead advocated for us to ignore them wholesale. I hope that my old team has better luck working with them than I did.