When I first received SSDI benefits I was filled with similar questions laced with paranoia about losing my benefits if I worked. I tried but also wasn't able to hold down a job for longer than a month. The information that I got directly from a SSA rep. was that I may go back to work without it effecting benefits as long as it is less than $1100 a month before taxes.
That's interesting about the ticket to work program because the literature on their web site states that it will not effect your benefits should you enroll in the program. I was leary on the program wondering how legitimate it really is and if it can get you in trouble down the line by putting you in line for a case review. They are very clear that it will not do this though. Check it out for yourself and see what you think.