Am fairly sure this is the right place for this post, if not, mods please move it. I used to work for the tax office (UK) and am constantly surprised when talking with other UK internet marketers that they don't know they can get a lot of their expenses written off and therefore deducted from their tax bill. Things like training ebooks, $7 dollar reports, software etc are all tax deductable. Even if you only bought a product so you could review it or sell it on, the initial outlay was an EXPENSE and should therefore be included in your accounts expenditure list. now, if you are making a full time living from IM then you really ought to have an accountant and they would deal with all this but a lot of people who are only making part time earnings and therefore don't employ an accountant aren't aware of this. So, keep every receipt you ever receive in relation to your business and when you work out your tax return, deduct them! Not sure if this applies to US business but I would think it probably does (don't just take my word for it though, check and stay on the right side of the law) as we have similar taxation systems.
Thanks for the tips, others might like to share useful tips; one I didnt know about (again may be UK rule) was that a retrospective claim for up to 7 yrs can be made for various items eg like computer equipment - for certain professions.