This review after two clean out bags...
I sent items to thredup after carefully sorting through them based on brand, quality, etc. they had already stated how careful they are to only accept things in good condition, so I made sure that there were no stains, no pilling, no stretching, etc. I feel it took a long time to process the bags... It took upwards of two weeks for my last bag to be processed. They accept very little. My first bag was full, and they only took 8 items. My second bag had a few more items with the tags still on, and they accepted those... maybe 10 items?
In total, I will receive a payout credit of about $31. However, due to the high volume not accepted, I requested my items be returned to me so that I can sell and donate them locally instead of having thredup recycle them. This costs $14 per bag. My total "profit" from thredup was not even $5. It should also be noted that the payout structure is changing 6/1/2015 and for small, less expensive items (like kids items) you'll only receive 10% of what they sell it at now (per their website).
Note that the site holds your payout for about a week. If you want to spend the money on clothing from Thredup, you can immediately use the payout. If you want a check or for the funds to deposit into PayPal, you'll have to wait quite a while.
For all the effort of sorting the clothes, sending it all in, then receiving it back when they don't accept much, it really isn't worth the effort. If someone has a bunch of unused designer bags laying around maybe they'd have better luck but it isn't for moms I know.