About a million.

I think that in general due to rounding — and more importantly, other real world factors which mean that megapixels only relate loosely to actual resolving power — it doesn't really matter if "megapixels" is binary or decimal. It is a useful term because it happens to be in the range where we get human-useful small numbers with the digital cameras (so far). It's rarely used to mean a precise value — one 16-megapixel camera will likely generate photos with a slightly different size than one from another brand.

For the same basic reason, "kilopixel" isn't a real word, because there's no particular case where it would be useful.

Overall, a lot of us coming to photography from a tech background, be it programmer, engineer, or otherwise, have a tendency to look for precision. When it comes to exposure, anything under a third of a stop is unlikely to be a big deal, and when it comes to pixels, a similar basic rule makes sense: until we're talking about doubling or halving the number, don't sweat it.

I originally posted this as a comment to another question, but I think it answers this one.