You guys are more lucky than I am. I rarely come across a shaking patch of grass, and when I do, it's usually an Audino or I never reach it in time. Not that I'm complaining, the extra Exp. Points from Audino are a great boost, but I would like to run into some other uncommon Pokémon in the various areas like... Pansage.
Sadly, I have run into the ripples in the water more often than the shaking grass, which is upsetting seeing as I don't have any access to Surf yet. >_>
I did come across quite a bit of dust piles in Wellspring Cave while looking for a Drilbur - who is currently on my team.