I've heard similar stories but there are no real figures out there as to how much trading is actually algorithmic trading. It reminds me of may 2010 when the Flash crash happened. While the source of the flash crash has never been nailed down it's believed that it was a fat finger trade (someone adding and extra 0 to a trade by mistake) that caused it. This then set off all the algorithms selling like crazy causing the a massive crash only to recover minutes later.
I think the important thing to remember about these algorithms is that they are trying to replicate human behaviour. It's humans that still make trades that move the markets and the algorithms try to spot when/if a big move is coming and trade accordingly.
I don't think you have anything to worry about too much because if push comes to shove you are smarter than a machine. It's just a case of out smarting the other humans that are also playing the markets. Figure out how to do that and you'll be a rich man.
Thanks for the post moonie. It's an interesting subject that's for sure.
May the markets be with you!
The Spread betting beginner