Just a quick update, in case anyone else is interested.

I did indeed get to swim at the Water Cube on Sunday (13 Nov). Some random notes:
* I didn't realize a subway station was closed, and ended up taking the line 15 to Olympic Green (purple on most maps). In the end, that was better.
* Not sure if this happens all the time or if there was an event, but you had to go through security and the entire block of the Water Cube & Bird's Nest was fenced off. On Sunday night, there was one entry, about 1/4 mile south of that subway station.
* The hours of the Water Cube are rather generous (even on Sunday it was open until 10pm).
* Cost to get in was RMB60, about $8.75 US (at this time). You need a ticket; the ticket booth was closed, but there were people outside selling tickets. I thought it was fishy, but I didn't have a choice, and it worked.
* It is a hike inside to the check-in desk to swim. They'll give you a locker key, and make sure you have a suit and cap (both are required). Goggles are optional. I didn't have a cap, but they had some loaners (I'd recommend having one, as these weren't that good)
* The pool was divided in half with something that resembled a fence. On one half the floor was elevated to only 1m deep, and anyone could swim there. The other half was 2m deep, and to swim there, you need to pass a test.
* The deep water test consisted of treading water (hands out of water) for 30 sec, followed by a 200m swim (any stroke, no time). The end lane of the deep area was dedicated to testing, and they had someone on deck who judged (he didn't speak much English, but had a laminated paper with instructions in English.)
* Once in a lane, be prepared for anything. I went in the, "fast," lane, which really wasn't. I ended up passing one guy about every 200m. I swam about 2500m, including the test.
* When I left, I made the mistake of following my phone's directions, heading to the Olympic Sports Center subway stop, then saw the fence, and remembered the security checkpoint. I had to backtrack, and go to the Olympic Village station, and then I took the Green line (number 8) to leave.

I stayed at the Doubletree hotel, near the Daguanying subway station. The cost to get there (I think) was RMB5 each way, but took a while...I'm guessing 90 min each way.

Note: I got the subway card, where you add/pay as you go (like an Oyster card in London), so I may be off with the subway fare.