This kind of lack of liquidity in the exchange itself is not a good sign. Today's arbitrage opportunity can be tomorrow's scramble for the doors. It is not sufficient that a few methods work, even if they are methods that you yourself use, if any of them do not work, and this affects the liquidity of the exchange, it is bad news. Without some stability to all the advertised funding/withdrawal methods I have to say I am out.
the fact that we discuss this rare arbitrage opportunities here and everybody is stressing to buy as fast as possible should be enough negation to your lack-of-liquidity-thesis. bitcoin is still a very small market. spreads are high, volatility is high, arbitrage is high (markets coordinates TIME and INTEREST according to Friedrich Hayek), and offcourse, where there is only a small number of traders, there is also a bigger delay in coordination (of time and interest).
btw: this thread just destroyed some asymetric information, therefore it helps lowering spreads, arbitrage and volatility. an possible (if i may assume that the most of us is acting rationally) increase liquidity, due to instant profit opportunities.
taking into account that bitcoin is traded 24/7 and that people sleep 8/7, have different timezones, don't look at charts and markets all the time, have no account at tradehill at all, or are simply wathcing several other markets, i am not in any way concerned.
the sheer mass of small and big bitcoin trading plattforms is to me a sign of increasing liquidity, not decreasing.
information is the key. information regarding big arbitrage has a certain value in BTC, in this case up to ~0,20 * 1000 BTC -> quite a lot.