Called the Gold Desk and have been waitlisted for a couple of flights I have later on in the year - September.
Anyone have any idea when these tend to clear? Is it much closer to the date or could it happen anytime from now?

My experience is well before the flight date, if there is availability. For example, I have a DXB - LHR flight on 16th March in Y, it was upgraded to J in November 2011. I am returning on 24th on a completely different ticket, paid Y, and that upgrade was confirmed in January.

I recommend calling occasionally if well before the flight, I have always been 'waitlisted' initially but soon enough you will be able to find out if you are the top, or how many are in front of you.

On the flipside, once I was waitlisted and it cleared 2 days prior (LHR-DXB and I still had tome to book the chauffeur).