If there were proof that bitfinex admins were front running or manipulating the trading engine to their own advantage, that would be a completely different story. But merely trading on their own exchange is a non-story as far as I'm concerned.
Please see here:
They are manipulating the trading engine to their own advantage.
https://bitcointalk.org/index.php?topic=660948.0;all
http://www.reddit.com/r/Bitcoin/comments/2t3p7f/xpost_from_rbitcoinmarkets_bitfinex_cso_phillip_g/
www.google.com/search?q=bitfinex+front+running+site:reddit.com
www.google.com/search?q=bitfinex+front+running+site:bitcointalk.org
Where is there any evidence that they are manipulating the trading engine? The first link looks unrelated to this, it talks about short squeezes. I don't know the details there but I do know this is a possibility when the price moves sharply and someone's margin position automatically is closed. The second link is the same thing as what's posted in the OP, and again that's an admission of an exchange admin trading on his own site (fine IMO) and not an admission of manipulation or front-running (not fine). The rest are google searches for which the top few hits link to the same reddit threads, I'm not going to dig through those. Anyway I've shared my opinion and unless there's evidence of actual manipulation then I think that's all there is to see here.