Today I unexpectedly received a K-1 form for shares of an ETF (US OIL
> FUND, symbol "USO") that I sold short in 2007. The form was blank except
> for my correct name and SS number, and had a printed note to call the
> issuer's tax office as they did not have my correct info.
So reading the posts here, you can ignore the K-1. But you might have paid interest to hold the position, and this could be deductible as investment interest (with the limitations and carryover as usual).