Symbian is going open source. This is a pretty interesting development, but I think it may be too little, too late, and it doesn't imply any major changes in the Symbian platform.
The real problem with Symbian isn't the fact that it's closed, it's the fact that it's Symbian. It's a difficult platform to develop for, its UI concepts are dated and accelerating towards antiquated, the "access point" scheme for managing IP connectivity is appallingly difficult for users, etc. Perhaps going open source will provide a catalyst for some serious changes and revolutions in the platform, that would be great. We'll see. Increasingly, the features of the Symbian platform that made it compelling are becoming unnecessary... the hardware platforms for mobile phones are no longer the exceedingly resource-constrained, battery-sipping environments they once were, and that will only become more true.
2010 is a long way off... the iPhone 3G ships in 3 weeks, Android phones this year. Developers finally get their hands on Symbian innards one year after that? I can't see that being very interesting to new developers.
It could be a huge boon for existing Symbian developers though, who've wished for access to deeper APIs, or even just to understand what is going on down deeper in the idiosyncratic Symbian brain. But again, in a year or two... it doesn't help now.