I'm not really sure how you're getting 100 ms. For someone on the equator, time = 2*d/c, which works out as 72000/300000 or 0.24s. Unless you're trying to access a server actually on a satellite, the data has to go up and back down again.

I was being lazy and pulled my numbers from wikipedia.[1] It seems that the calculation there takes into account latitude of the transmitter and receiver, and so gives a slightly larger number. For non-equatorial ground stations, latency is higher.

In the context of communications, it's important to clarify what "round trip" means. The latency to send data from one ground station to another is, at best, 240 ms, but the time taken to request data and then receive it is going to be twice that. In practice it means that if you were browsing the web over a geostationary satellite link, it would take 1/2s between clicking a link and receiving the first data back from the server.

[1]: http://en.wikipedia.org/wiki/Geostationary_orbit#Communicati...