Some ETNs may implode soon?

Mostly, though, they are either derivative-based (ie. futures) or leveraged or inverse indices, not simple long-only asset-holding indices. INP is an exception.

Sometimes there are advantages to the ETN structure as opposed to the ETF or mutual fund structure. In particular, that's the case with respect to tax treatment on certain kinds of gains (again, for example, futures contracts). By tracking an index rather than holding derivatives, and simply holding the ETN long-term, gains which could otherwise have been taxed unfavorably may be turned into long-term capital gains when the ETN is ultimately sold. The downside, of course, is the expenses which get lopped off - sometimes quite high - and the fact that you are exposed to the credit of the issuer. As noted in the article you linked to, folks who were on the other side of such a note issued by Lehman got hurt very badly a couple of years ago.

It's often noted in the *name* of the security. For example, and this is a good one, the iPath DJ-UBS Commodity Index TR ETN (symbol DJP) is an ETN.

Moreover, there are are other "ETF"-like securities which track similar commodity indices, but several of them are yet another flavor of pooled interest -- they are structured as partnerships like US Commodity Index (ISCI) and buyers of them may get K-1s for tax purposes and be hit with annual taxable gains (at 60/40 long/short term) regardless of whether they sell the fund and without having had any cash distributions along the way. Again, the up-side to the ETN structure is avoidance of most of these tax issues.

Another example, JPMorgan has an MLP-index-tracking ETN for similar reasons, though less about tax costs and more about administrative issues -- and they make it very clear that the ETNs are "senior, unsecured obligations of JPM Chase&Co."

(Another advantage is that the ETN can go into an IRA, while buying MLPs directly in the IRA may lead to problems with Unrelated Business Income ("UBI") and potentially your IRA would owe taxes.)

Anyway, there are certainly potential advantages to the ETN structure which may offset the credit risk.

I'm not sure there's a "quicker" way - but I strongy recommend that if you own something you know what it is. If you have something in your portfolio and you're not sure if it's an ETN versus a regular ETF versus a partnership "ETF", you probably shouldn't have it in your portfolio.