Market Share As of 1 March 2007, NYSE Arca is the second largest Electronic Communication Network in terms of shares traded. Approximately one out of every six shares traded on the American financial markets is traded on the system. For New York Stock Exchange-listed securities or Tape A, it accounts for just over 10% of the shares traded. For NASDAQ-listed securities, NYSE Arca accounts for approximately 20% of the trading volume. For exchange-traded funds, NYSE Arca accounts for 30-40% of the traded volume. http://en.wikipedia.org/wiki/NYSE_Arca
Don't think that DOMS or ARCA are only one person or a group of shady market makers. That's just the platform that's been used to trade shares...