Catherine Austine Fitts wrote a detailed analysis of the SLV (and GLD) structure some time ago now. The paper It is doubtless the benchmark study of these dubious vessels.
Like so many ponzi paper precious metals schemes, GLD and SLV are all about undisclosed risk, conflict of interest and complete lack of regulatory oversight.
Slowly the market seems to be coming to terms with the risk of these schemes though. When she wrote the article a year ago, the trading discount to those ETF's with real metal (CEF, GTU) was up to 10%. These days the market is discounting SLV and GLD compared to the premium of the real silver ETF, PSLV (Sprott Silver ETF) to a spread of up to 22%. I wonder what the discount will be when things hot up?