I think what you are asking is if you should report to the IRS (file an income tax return) small income that you earn every so often. Am I reading your question correctly?
At the end of the tax year you will add up all your small revenue streams, and subtract any business expenses. If your net profit is over a certain dollar amount you must file a tax return with the IRS. If you do not meet the dollar threshold for the year, then you do not need to report your income to the IRS. I believe the minimum you can get away with earning as a self-employed person without having to file a tax return is $400, but I'm not an accountant, so please double check with one. From the instructions for the 2010 Schedule SE (Form 1040):
You must pay SE tax if you had net earnings of $400 or more as a self-employed person. If you are in business (farm or non-farm) for yourself, you are self-employed.
The instructions for the 1040 also state that you must file a 1040 if:
You had net earnings from self-employment of at least $400.
(See page 9, Chart C, #3 of the instructions for the 1040.)
Now this doesn't mean that you'll have to itemize every one of these tiny transactions on your tax return. You will just need to group them into income categories. This shouldn't be too difficult to do if you are already tracking your finances in accounting software.
Also, even if you don't hit the $400 threshold, you may still want to file a tax return if you have business expenses you can deduct.