I think that this is interesting for a couple reasons.
First of all, it's proof of how bad software "patents" actually are. A good part of the community has known for a long time that patenting things like "double clicking", "tabbed interfaces", and "icons" was a bad idea. Every programmer here has likely violated somebody's patent in code they've written. So far, the only saving grace is that nobody has enforced this. If Microsoft goes through with this, hopefully it'll raise awareness of this problem enough that the patent system will be reformed.
On that point, this also shows that software patents can help companies enforce a monopoly. If Microsoft suddenly throws down the patent on windows, icons, tabs, and the "e" key, any company using them may be forced to pay ridiculous extortion fees (err, license fees) or, basically, shut down. That's basically how a monopoly works.
Second, the fact that Microsoft, after all these years, has finally revealed their hand shows that they're scared. You don't hold your cards for 10 years then finally throw them on the table for no reason. They're beginning to see Linux as more of a threat, and now they want to do something about it.
In any case, unless somebody withdraws or settles, I don't see this being over for a few years at least.
