There's no such thing as too much. When your deductions/donations are greater than your income, that could increase your audit risk, but many people spend years gathering items and then donate them to charity and that amount could very well be more than they're income. So it's not an unreal situation.
Last year you only needed to provide receipts of donations if the donation was greater than $250. In 2008 the IRS changed that law and made it mandatory that ANY donation, even $1, must have a receipt.
If you donate clothes (or any item), the place you donate them to will issue you a receipt stating the fair market value and the general type of item. That is the amount you can deduct.
It is true that unless it's very high it won't raise a red flag - I've heard claiming more than $5000 every year is bad. You might claim a lot one year and not the next.
But to clarify re receipts - all donation sites will give you a receipt IF you ask for one, but in my experience it NEVER includes an estimate, no matter how much you've donated (including a computer, dozens of bags of clothing, furniture...). Keep track of each item you've donated in your own notes, and give your best estimate for each item or use the Its Deductible feature
There is no limit to how much you can donate. You need to make sure you get a receipt from the charity (even if it is blank). Make sure you have a list of everything you give, attach it to the receipt they gave you and make sure it is dated. TurboTax gives you several ways to estimate the value of the donation. Using the list you kept, you should be able to come up with a value.
Remember, it is not the IRS that will determine the value, you need to (kind of like guilty until proven innocent). Make sure you have the documentation to justify what you donated.
You need a detailed record of the items donated and their condition along with their value. You need a receipt from the charity you donated to with the date and general description of the items. You can use thrift store selling prices, ebay, or It's Deductible to set the values. You can look at IRS Publication 1771 to get detailed information.
You should be using www.itsdeductibleonline.com for valuations. It's free and seamlessly imports into turbotax. DO NOT USE the valuation sheets provided by the organization as they are always always always 30-40% LESS than fair market value...because they list the values as to how they sell them in their retail stores. Do not accept any organization's approximate valuation as one, they are not permitted to provide an approximate amount, and two, for those that do provide an amount, it's VASTLY less than fair market value.
I have always done my own taxes. The first year we had a house I used an accountant. When it came to deductions he put down over $2000. I was surprised but based on line 7 income level it was less than 2% of wages. I donate close all the time with two small kids and usually hit the dump bins no receipt. My own rule of thumb based on what the accoount did was to make sure perecnt wise it was too large based on income. I usually figure a number of around 1.5% of wages unless we had a large single donation with a receipt.
in answer to cnkkrebs about the bins you donate to like planetaid, etc. Normally there is contact info on the bin that you put your clothes in, etc. Contact them and they will send a receipt. I actually did this for PlanetAid and they were great - I just told them the donation date and they sent it directly to my house. Good Luck!