Ah, yes, I am very guilty of this. In fact, I just returned a few things I bought a few months ago because they were still hanging in my closet with tags on, and they were fall/winter items. I also have a pair of red Frye cowboy boots that I bought in December (Merry Christmas to me!) that I just can't decide if I they will be comfortable or not.
As for return policies, I do tend to shop at places with generous return policies.
Zappos - 365 days to return an item (which is why the boots haven't gone back yet)
Nordstroms - don't actually know their return policy - but I've never had to show a receipt...unlike Zappos, I believe you can wear an item and then decide to return it (like shoes that turn out to hurt your feet)
TJ Maxx - I think it's 3 months - with a receipt gets you a full return however your paid for it, and after that you get store credit for the full amount. If you don't have a receipt and it's after the 3 month mark, you have to accept whatever the item has been marked down to in store credit
Don't know other policies off hand.