I brought this same issue up on
another thread, and it is precisely why I no longer use Omnifocus on my Mac or iPhone (despite all the $$ I paid for both!)
But I do think both sides of this argument have good points.
One one hand, it is a common business strategy for commercial software companies to restrict compatibility and force customers to buy their own stuff, so it's always a good idea to investigate a commercial product's interoperability before purchasing it.
On the other hand, the way we use software and the internet has drastically changed in the past few years. We're evolving into a network-centric world of cloud computing, enterprise architectures, and mobile applications. It's becoming very evident that flexible software with open-source APIs and maximum interoperability (like Google, YouTube, Facebook, etc) are beating out their "stove-piped" competitors. We are approaching a point where one should
expect interoperability from a product, or at least expect it to have a "web version".
I think Omnifocus is hands-down the best GTD software application out there. But I use Toodledo now, simply because a) I can access it anywhere, and b) it syncs very well with MS Outlook on my office PC, and c) there are many iPhone to-do apps for Toodledo that I can choose from. Total cost for all this? $0. But if Toodledo did charge a price, I'd have no problem paying because it works everywhere I need it.
Omni Group has publicly stated on these forums that they are Apple-biased, and the fact that they have not responded to our concerns suggests that their lack of interoperability is intentional. After all, how hard is it to publish a simple API or generic XML interface?
I'm really hoping that OmniFocus will one day decide to play nice and publish an API or at least restore that OF-TD script. It would be futile to develop a 3rd-party API unless you had time to maintain it so it doesn't break with each Omnifocus update. So until Omni Group changes their business strategy, I'm working just fine with Toodledo.