We'll fly out of SFO mid-day on Tuesday, August 12, arriving London the following morning (the day before Worldcon). We're staying at the Crowne Plaza at the far end of the ExCel complex. (This means no casual running back to the hotel room, of course.) The day after the convention (Tuesday), we move to the Intercontinental Westminster for two nights. Yes, it means changing hotels mid-stay, but I'm using the free-night-any-hotel-in-IHG offer, so it seemed like we should use that on one of the nicer London hotels in the group. On Thursday, we move to the Holiday Inn Express Southwark for four nights. Because our flight back to the USA is at 10 AM Tuesday morning, we'll move again on Monday, spending the night at the Heathrow Holiday Inn so we don't have to fight commuter crowds to get to the airport on Tuesday morning. Thanks to time zones, we get back to SFO mid-afternoon the same day we left. I doubt I'll be in condition to do much the following day, however, and even though we're staying in a hotel near my office the rest of that week, I don't expect to go back to work until Thursday.
We haven't completely made up out minds about all of the things we want to do. We're considering getting a 3-day London Pass because when you add in the cost of a 3-day Zone 1-6 Travelcard, we figure it's at least a break-even, and it saves the hassle of buying individual admissions. Also, once you've bought the pass, it's easier to say, "Let's hop on the Thames River Cruise" or "How about we pop in to the London Canal Museum" or whatever.
Items on Lisa's top list are Churchill's War Rooms, the HMS Belfast, and the London Transport Museum. After that, we'll have to have a look at what's available in the guidebook and how much energy we have. (And there are mechanical things like we'll probably have to do laundry at some point early in that period; I hope I can find a laundrette near where we are.) Besides those three core days of attraction hopping, there are other things more train-related that we might try to do on the weekend, such as the Epping Ongar Railway, the only preserved railway you can reach on the Tube.