I used to have this setup and it worked nicely. I had a three-way sync: Omnifocus (Mac) <--> Toodledo(Web) <--> Microsoft Outlook (PC). It was great because I could manage tasks from work, home, the road, or anywhere I had internet access. Also, from my iPhone I could use several different apps: OmniFocus for iPhone, Toodledo's iPhone app, or many of the other apps that sync with Toodledo (such as Appigo's Todo).
The weakness in this setup was that I relied on an
OmniFocus-Toodledo script that allowed OmniFocus to sync with the cloud. However, on the developers' website they stated that they did not plan to maintain it, so I knew it was a matter of time before it would stop working.
And sure enough, my perfect GTD environment came crashing down when an OmniFocus software update (sometime in mid-2009) rendered the OFTD script useless.
As much as I love OmniFocus, I can't use it if it's not interoperable with my PC world, so I had to stop using it. Now I just use Toodledo's free web service. It allows me to sync to both my iPhone and my PC (Outlook). I can use it on a Mac from a web browser. Sure, it's not as elegant as the Omnifocus app, but it works.
I'm hanging out on this forum in the hopes that someone will either update the OFTD script or write some other kind of API that will make syncing to Toodledo and/or MS Outlook possible, because I paid good money for the Mac and iPhone apps and want to start using them again!