Firstly I have to declare I have never tried what was asked, but I have read the quote from CTC referred to by Big John above but it doesn't seem logical to me especially where it suddenly refers to rear mechs. I am more inclined to trust Sheldon Brown (
http://www.sheldonbrown.com/speeds.html), who said:
"Chain. As you go to more sprockets on the cassette, you need a narrower chain. However, using a narrower chain with an older system rarely presents any problem. Thus, you can use a "9-speed" chain with a 7-speed or 8-speed system, or a "10-speed" chain with a 9-speed system. Since the chains designated for more gears are usually more expensive and don't last as long, this is not the ideal approach, but it's perfectly workable."
The reason why Sheldon is likely to be right is because there is very little difference between the sprocket thickness of 7/8/9 speed (1.75mm to 1.9mm) and 10 speed (1.6mm to 1.7mm), depending on brands etc., and similarly for such chains' inner plate width (which are typically between 2.15mm to 2.45mm). The big difference for the chains is in the thickness of the chains' plates and pins' width. Typical width of 7/8 speed chains are 7.1mm, 9 speed chains are 6.8mm, but 10 speed chains are much narrower at around 6.2mm.
Bearing in mind that the great man never said you can use a 10 speed chain on a 8 speed system, from the dimensions I suspect it will probably work but it may be tricky to get it indexed nicely. There is also more risks for the narrow chain to fall between the chain rings.
If anybody has tried, please do post their experience.