"Once they have gained enough attention from developers, how might they change their position?"
I share your concerns in that sense that we should never forget that in the end Microsoft is a corporation which does what a company usually does: making money. However, I also think its important not to endlessly continue to hold their reputation against them. I'm not saying we shouldn't keep it in mind, but we also shouldn't completely focus on it either.
And I think something important has changed when you look at the past. Back then MS philosophy seems to have been "here's our product, take it for what it is!" and as soon as someone got too close they got on the offensive part, at least it sure appeared that way.
Take projects such as Samba; trying to get Linux "Windows network compatible" (to put it /very/ easy). It became apparent from multiple sources that Microsoft was at the very least worried about the project development. Yet nowadays they even started to contribute to the project itself by donating source code (so I've read anyway).
What to think about Mono? .NET is a very important asset for Microsoft, its totally intermingled with their operating systems as well as their Office environment. .NET is to Microsoft what Java was to Sun (at least that's how I look at it). Now some "open source hippies" try to "steal" the glory by trying to "push" .NET onto environments which it was never intended to ? Heck; it even "targets" Windows itself.
What does MS do? Promises not to take it out on Mono through patent issues (granted; such promises can be changed on a whim). Heck, in several ways they even seem to encourage its development. The reason why I think this to be mention worthy is the origin of Mono. While it is an open source project it wasn't merely started by a group of .NET fans who wanted more out of it. Instead, it was heavily backed up by several companies. And companies, as we all should know, /always/ have their own agenda in the end: Making more money.
Yet MS didn't go out on the offense. Even though they probably could have; take a look at how they use Linux to "attack" Android with their patent claims.
SO summing up I think you're right that we shouldn't forget about the past. But we also shouldn't ignore the changes within Microsoft either.