Engadget reports that the Lenovo IdeaPad S10 (not yet available) runs what looks like an average keyboard-side surface temperature of 104 degrees F. If accurate, this is incredibly uncomfortable to use. My old Dell Latitude D600 notebook used to run about 100F on the palmrest area over the hard drive. It was so uncomfortable at that temperature that I ended up getting a USB keyboard for my office (it was my main computer). The Dell Latitude D620 that replaced it a few years later ran at much cooler and more comfortable temperature (around 90F, if I recall correctly).
My Acer Aspire One has gotten up to 96F which is pretty warm itself though a considerably cooler than the Lenovo S10. The one advantage both netbooks have over full-sized notebooks like the D600 is that their small keyboards mean that you will probably not actually use the palm rests. So, these surface temperature are not as much of a problem as they are with notebook PCs.