Mander, I have a space bag in my basement filled with old concert tees (Siouxsie and the Banshees and R.E.M., anyone?), as well as tees from the radio stations where i worked. They don't get worn, but I couldn't bear to part with them. They're probably worth a little something as collectors items.
Diana, I like that "thievery" test -- I'm going to try that.
I tend to relegate items to second-tier status (my knocking-around-the-house clothes), but then they seem to hang around way too long. Honestly, how many of those things do I need? I'm getting more selective. I just put about half a dozen tees and casual knit tops in the Goodwill bag because they're starting to pill or fade. I wore them some last year under cardigans or hoodies, but I can tell that this is no longer going to cut it for me.