If I'm informed correctly, IQFeed / DTN.IQ provides unfiltered data. While this may bring some advantages because no trade is lost, several users have complained about artificial "spikes" in the data. Last summer some users even said that there were such a high number of spikes that IQFeed's historical data was almost useless for charting, in comparison with eSignal. But I also remember that an IQFeed representative mentioned some months ago that IQFeed was planning to implement filters (activatable by the users) in order to allow users to filter out unwanted trades outside the bid/ask range. So maybe the situation has improved in the meantime. My question is: How is the IQFeed data quality now? Is IQFeed's historical data good/accurate enough to be used for charting or backtesting of trading systems?