As a rather large body of water is headed Bangkok's way, likely to coincide with a spring tide, there are some pretty reasonable concerns regarding the likelihood of flooding there.
We've two writers based in Bangkok and they'll be working over the coming days to put together updates as the situation unfolds -- the first entry is up now on the Bangkok blog here. As Brock says, the main touristic areas, at least at this stage, won't be too badly affected, but other areas will be.
Have also heard that buses are no longer running from the Northern Bus Station, but I can't find the news-link for that just now.
Anyways, keep an eye on the blogs and I'll repost anything important into this thread.
Likewise, if you're in Bangkok (or Ayutthaya -- which seems to be very badly flooded) do feel free to post in any advice!
Hope you all keep dry - and watch out for dodgy wiring in the floods.