What Jim said, fighting Doc Brown. I don't wear hats, so a Mario hat gets a big meh from me. Might be a different story if there was a good Yoshi doll, though.
I remember an IGN article saying that if you think the prizes will be good, go ahead and gather as many points as you can before they're reset for next year. Otherwise, lay off and let it reset so you can quickly gather points for next year. I haven't read much about Club Nintendo in America, but it seems stupid that all your hard work can go away once a certain date hits.
Although I never participated in Super Power Stamps, I wish those would come back. Big catalog to choose from, buy whatever you want once you had enough, no resetting of points, and I just thought those physical stamps were cool. I forget how you got the stamps, I think it was a lousy process (I'd prefer the Club Nintendo approach of doing surveys), but whatever. I even forget if you were ever able to buy those items with cash... I think you could, like there'd be a cash value and alternately a number of stamps.
I'm mainly just grousing that the stuff I saw in the Nintendo catalog was never as cool as what Japan got with their Club Nintendo. And from the looks of things, America still has yet to catch up. But I did like that Mario SMB2 wallet...