Today I've been working on a "Early Warning" workflow designed with SharePoint Designer. It is supposed to run on every item change and to suspend itself until few days before item's expiry date (it's just a date column). But, it didn't work as expected.
I remembered reading that there are some glitches in the way Workflow Foundation dehydrates and rehydrates the "sleeping" workflows. There is a patch available at http://www.microsoft.com/downloads/details.aspx?FamilyID=6096ce0f-d21e-47ac-afe2-d4e1c2fce670&displaylang=en.
I downloaded it and it worked like a charm!