What happens when Income tax is filed after filing deadline?

I e-filed my 2009/10 (Assessment year 2010/11) tax return (ITR-1)on 18 April 2011. There is no balance due or refund on the return and my salary income was well below than 1,60,000. I just wanted to learn how to file a tax return so that I could do it myself for 2011/12 assessment year tax return. Please advice if I would be liable to any late filing penalty?