Well, the biggest sign is that payouts do not occur or are significantly delayed without a valid reason (i.e. coin hard fork & new wallet release or blockchain issues).  Basically, if something only happens on that exchange, but not on others that carry the same coin pairs... get your coins out ASAP!

As an investor, I wouldn't bother.  I think this may have been presented better - the idea is not to start using Bittrex as your wallet... that would be a bad move (just as it is a bad move if you have all your BC on MintPal, Cryptsy, etc.).  The idea is that if you are actively trading BC (selling or buying) try to do a little more of your business on Bittrex rather than just doing all of it on Mintpal or Cryptsy.

I have major reservations about Bittrex myself.  Don't get me wrong, I'm not questioning their stability or security... simply that I have a problem with the pay-for-pairing model of exchanges these days.  I have exactly the same issues with poloniex, Mintpal, and to a somewhat lesser extent Cryptsy (I have much bigger issues with speed and reliability as far as they are concerned).

I have great hope that the upcoming BC-centric exchange will resolve these issues for myself.  The simple problem is that we're literally drowning in shit-coins... and these "give me 1BTC and I list your coin without question" exchanges aren't helping things at all.  We need more exchanges with extremely high entrance requirements (i.e. must be at least 3 months old, must have at least $1M US in market cap, active development, etc.).  

Those are the sorts of statistics that show a coins true colors... not the fact that the devs or community can scrape together a few BTC to buy their way in to an exchange.

I certainly hope those without the capital (either BC-wise or BTC-wise) do not just blindly stick all of their coins on any exchange - including Bittrex.  We do need liquidity, but we don't need people that easily panic or cannot afford to lose coins in bad trades filling up the exchange just to look good.  I'd rather never see a BC secondary market than see a bunch of small BC portfolios lose coins.  Never put anything on an exchange (any exchange) that you cannot easily afford to lose.