At lesat once a week I receive an inquiry from someone wondering if they will lose their SSI if their SSI if they work a few hours. The answer is that Social Security does not look at the number of hours you work but rather how much you earn. Essentially you cannot earn more than $1000.00 a month if you wish to keep your SSI. If you are blind, the amount is $1640.00. I have posted a Fact Sheet for 2011published by Social Security which contains all of the numbers for 2011.
If you think you would like to try working again but do not want to lose your SSI, Social Secuirty has a program called Ticket to Work which can help you try and re-enter the work force without losing your benefits during your attempt.