arinesmith - Yes, if you have the online account and the Fitday PC and you are a Premium member the sync feature syncs everything on either of your accounts.
So if I am at work, and I enter a custom food into my online version...I can sync when I get home and that custom food shows up in my PC version...and vice versa.
As long as you sync regularly, your data should be the same in both locations (online and PC).
Hope this helps
I find it extremely convenient!