I adored my stay at Park Lane Sheraton last July! It was a very nice hotel, I got a good deal and my only complaint was the lack of good air conditioning. (I was there on what was, at that point, the hottest day of the year.)
I loved the location- I landed and walked to Harrodd's to buy the new copy of Harry Potter, just released that day and then back to the hotel to sleep. I found the staff eager to please and the room was comfortable and well appointed. I did not care for the European King size beds- they are two twin mattresses in a King bed frame, but that was everywhere I stayed.
I am considering returning next Spring (no air conditioning problems anticipated) and will defintely stay there again. It was so well-located that I never took a cab the whole time I was with them. I did move to Sheraton Belgravia (also a VERY nice hotel, I would say a step up from Park Lane) but the location wasn't as nice.
Also, they're offering points as Platinum ammenities now (for those of us who already have a few replicas of the double-decker bus) and the High Tea in the dining room is wonderful, even though I don't actually drink tea.
I think you'd enjoy Park Lane, but if you're going during hot weather, be prepared for old air units that work at about half capacity. The 1st thing I did when switching to Belgravia was enjoy the two air conditioning units in my junior suite/room- I blasted them until the room was chilly! But, Park Lane did give me a fan so that helped, and as I stated, the location was perfect.
Also, the Skyline Sheraton at Heathrow was very nice for a place to stay before and after flying in and out of the city.
I'm envious- have fun!