I really appreciate my iPhone's ToDo.app and my Firefox-rendered ToodleDo task list. Problem is, they've stopped playing nice together. From a post I wrote to the Appigo Todo Google Group:
I sync Appigo ToDo.app with Toodledo.This is what could kill Appigo's superb iPhone apps. If Apple ever produces a task tool, even if it's much inferior to Appigo's product, they'll have the huge advantage of controlling the MobileMe, iCal and iPhone data models and the message model.
Recently, I'm having problems. They're nasty because I can tolerate a lot of bugs, but I can't tolerate sync bugs that cost me data.
The details of my current problems aren't all that important to this post. I'm seeing items on ToDo.app fail to move to Toodledo, and I'm seeing changes made to Toodledo be reversed on sync with ToDo.app
That's bad, but the real problem is -- who owns these problems?
They could be Appigo bugs, Toodledo bugs, or emergent bugs shared between the two. I wouldn't be surprised if the problems I'm seeing are all three!
I'm a paying customer for both Appigo and Toodledo -- but I don't want to file two bug reports.
My gut sense, and I have some experience in my real job to support this, that sync is very hard when one vendor controls both ends of the transaction. It's damned near impossible when two vendors are involved.
Real soon now we're going to have to get to a situation where one vendor is responsible for the end-to-end transaction -- or Appigo is going to have to get extremely close to either ToodleDo or RTM.
In the meantime, who will own these problems?
I'm hoping Appigo finds a solution, but it's a damned tough problem. This has broken many a company.
 See HL-7.