It's Best to Check-In and Check-Out in the Executive Lounge
I've been staying at the Sheraton for 2-3 weeks every year. I'm very happy with the hotel and how it treats me as a Platinum.
I've found that the best service occurs by checking in and out at the desk of the Executive Club rather than in the lobby. The attitude tends to be very positive and they always try to upgrade to a suite. If there is no suite available on day of arrival, they will do everything they can to accommodate when a suite becomes available. The staff has been well-trained in treating Platinum members properly.