To suggest Google Instant, scroll down to the bottom, and under "I have another idea", select: Interface and settings > Gmail interface > Search options. I've j

To suggest Google Instant, scroll down to the bottom, and under "I have another idea", select: Interface and settings > Gmail interface > Search options. I've just suggested "Google Instant mail search". (I assume you can just suggest under Other, but I think Search options makes the most sense.)