Slightly off topic, but Vanguard ETFs are actually a share class of the corresponding Vanguard Index Mutual Fund. They *can* carry a tax liability of the mutual fund inside the performance of the ETF. Structurally that is the case, but it has yet to be a problem.
An ancillary benefit (for americans) is that if you owned the index mutual fund from vanguard, you can convert to the ETF structure tax-free, since it is just switching from a share class of the fund to another share class of the same fund.
Just sayin...