Let's say I am an owner of gold and a seller of gold certificates. People would like to use gold, but it's hard to buy and sell things with it. I am honest; and trusted (people already buy my certificates).
snip
This would be utterly pointless.
If people have to rely on a central counterparty to redeem their certificates for gold (or anything else - people have proposed that share registries might be maintained in a bitcoin block chain but again that would be pointless) that central counterparty might as well maintain the database of who owns what. There's no benefit to having a complicated distributed database like bitcoin for that when all the risk is already concentrated in a central counterparty. If your central counterparty is going got cheat you then they will. If the government forces the central counterparty to take some action then they will. It doesn't make a damn bit of difference if the central counterparty keeps the records of who owns what in a simple spreadsheet.
But the central party doesn't record who owns what - it needs to be trusted only in so far as it issues certificates (or bitgoldcoin) only up to the value of what they hold in their vaults. As the OP stated, you have the advantage of being able to transfer it to whoever you want via the internet.
That the central party needs to be trusted, or can be shut down by governments is a disadvantage compared to bitcoin - sure - but presumably it's the transferability, non-revocability, and double-spending protection that is the benefit.
It's not so great from a purely libertarian perspective, nor from the point of view robustness and points of failure/attack - but it's a far cry from utterly pointless.