I did not know that. To be honest I never come to these forums before, unless a major Pokemon game comes out, and I only glanced at the topics and didn't find anything about it. Where is your topic?
Also it doesn't take that long really. I personally think it's completely random. I've gotten a bunch of fossils now (my friend in Soul Silver only smashed rocks for a good 20 minutes and found a Dome Fossil).
Later on in the evening I found a Max Ether, that and the confirmation from msdfabio proves it's not just in Soul Silver as I thought. *updates first page*
@Late - It's an HM, ever since I think Ruby/Sapphire/Emerald.
@msdfabio - I'm thinking that it might depend on the area as well. I'm going to Cianwood later to check out those rocks and see if I find anything different or the same.