An automated online trading site which gives out credits for items which you can later redeem for refined metal, keys, other hats or whatever... also it allows you to put up an item and name your own price for such items that are hard to get (unusual hats mainly).
how does this affect me?
If you don't trade, it doesn't affect you at all. If you trade only in small amounts with people you see online then it doesn't affect you much at all... it really only affects you if you are hardcore into trading and need TF2WH to be there to let you unload your crap or buy stuff you want with your credits.
Indeed. The system for building up trust is atrocious to poorer players/accounts, as they have to make 15,000 credits, over 3 Refs' worth, in one week in order to move up in tier.
Yet, thanks to that item limit, the 15,000 has to be made with the sale of 10 items or less in one week... And the credit counter resets every week. -.-
Essentially, if you're thinking of ever getting out of Tier 1, selling any significant amount of cheap 225 credit items like the normal weapons is out of the question. And just to put it in perspective, thanks to the credit limit, you'd need to spend a whole month boosting your tier each of the 4 weeks just to be able to sell a Max's Head, whereas before you could do it instantly.
Valve's reduced the site to a slug's crawl (and it was pretty slow in it's default state as was) just because one of their bros couldn't keep some script kiddies off his tail. Casual traders can't build cred and hardcore traders can't sell anything expensive... TF2WH has a foot in the grave at this point.