I have some experience to share here too: I am also taxed at source, and have moved from Solothurn to Zurich sometimes in 2009. Then, in spring 2010, the tax authority (Finanzamt) of ZH sent me the forms for the tax declarations. I knew I did not earn above the limit where you need to make a tax declaration, and I went in person to them and brought them a copy of my tax return (Steuererklärung) for 2009.
All seemed fine, the guy with whom I talked was also puzzled as to why I was considered for tax declaration; he made a copy of my papers, advised I speak to the Kantonal people too (not just the city of Zurich). Which I did. But it didn't help, as I kept receiving reminders (Mahnung) to send said tax declaration...
Well to make a long story short, what had happened is that they had based their calculations on my earnings for the few months in Kanton ZH, and "normalized" that to what I would have earned during the whole year, somehow including the 13th salary as part of the monthly income, and came up with too high numbers. They didn't let me off the hook until I sumbitted a tax declaration - and I am still waiting for their answer on that one, as apparently they owe me some money