I don't want to appear "perfect" but I always declare everything, but also make sure that I wring out every possible deduction by saving receipts all year round (yes, even for a $3.99 ream of paper!).
I did work for a tax attorney for about 6 years and although I might have been tempted before to not declare something (although then I wasn't working for myself, so the point was moot), just like people will keep extra change or not let the cashier know if they've missed scanning something, I now would never "mess with the IRS".
Having seen so many people go through so much disruption of their lives and businesses because of the IRS tactics and ways of dealing with people they suspect of tax evasion, it is definitely not worth the relatively small amount of money you may save. Would you like a lien placed on your house and your bank accounts totally frozen without notice, over a matter of a few thousand owed in tax? Another thing a lot of people don't realize is that Tax Court is a totally different animal than the regular court system, with different rules of evidence and different rights (almost always on the government's side) - it's almost as if you are assumed guilty until YOU can prove you are innocent and meanwhile, your business goes to the dogs.
My other piece of advice is that if you do somehow wind up in trouble with the IRS, unless you are totally innocent and want to fight them on it, even if you can't afford to pay what you owe, talk with the agent about working out a payment schedule. Basically, unless you have a really nasty agent, they want to settle cases and get the money eventually, and most are quite willing to talk settlements if you approach them correctly. Just don't piss them off
