I too have noticed that the bottom grates get pretty distorted on the Performers. I think it's the combination of the upward heat of the burner flame and the downward heat of a chimney full of charcoal. Right in the middle there is some pretty intense heat, I imagine. I replaced the bottom grate on my Performer last fall, and it's already getting all wiggy.
And jkolantern, you can still get those old-school wire-style coal baskets from Weber if you like. I can't find the part number anywhere, unfortunately, but they will sell them to you. Or if you prefer the newer stamped-metal style, I've got a hot tip: Weber will sell you a set of them in a retail box for like $18/pair, or if you purchase them individually you can get them for $3.75/apiece. The stock number for the individual baskets is #62423.