Jenny -- a home office is a legitimate deduction! Don't give the government any more of your hard-earned money! If your CPA is cautioning you from taking this deduction he may not be the right CPA for you, or your home office may not meet the simple IRS requirements.
DemosL -- what is this 24-hour clock percentage thing? My office occupies a tad over 27% of my house and my accountant deducts that percentage from utilities, property taxes, and so forth.
One important point to remember about a home office is that you need to stop deducting it 3 years (I think that's the correct number) before you sell the house or else the IRS will dink you for your previous deductions.
Want to have some fun with your CPA? Get into a discussion with him or her about the Flat Tax! Mine almost stroked out trying to convince me that our current system is so much better!