I suppose some people have issues. I've had good luck with mail in rebates dealing with gigabyte through newegg or tigerdirect. It does take a month or two to get the rebates, but in my case I got 2 $40 rebate gift cards so it was well worth it. Only once did I not get a rebate, called and contacted the rebate center and resubmitted and they made good on it (xfx). I think I've done around a dozen or so mir's and saved quite a bit of money. You do have to follow the instructions though which are typically simple like the upc off the product, a copy of the invoice proving purchase and date (that it fell within the rebate period), mailed on time, mailed to the proper address etc. Basic following of instructions and understanding rebate restrictions (such as limited to 1 per household etc).
Pcpartpicker is good for a rough idea but they're not always the most current or accurate. Sometimes parts get listed as compatible when they aren't, sometimes products aren't listed as if all vendors have stopped carrying them yet you'll find it available on newegg's site which being a pcpartpicker vendor should show in their listings. Best to get current prices from the vendor pages themselves (ie, newegg, amazon, ncixus etc) which will show accurate pricing and discount, sale or mir status.