We have used the GRSS auction feature a few times now and are very pleased with it. We have noticed what seems to be a big problem though and we would like to see addressed. We count down over vent when we're going to be closing down the bids and people try to ninja bids in and it causes resentment.
We would like to see a timer (perhaps optionally enabled) which triggers when the "Stop Bids" button is pushed. A raid chat message could appear with a count down. If a ninja bid comes in, the counter is reset and starts over at whatever the beginning was. Say 5 sec for giggles. This gives an opportunity for those that wish to counter such a bid to do so. I would say this is a feature that I'd like to label as necessary for us. Or at least some similar mechanism that counteracts ninja bids.
Another, less necessary feature is to reject bids that exceed a user's available DKP. Though this can be manually managed so it's not that big a deal. The auctioneer can reject a bid already, so it's just a nice-to-have.